Hi,
I am trying to reshape this data, so that I have Country and Year both as a Columns. I imported this data from an excel spreadsheet.

Here is my Code. I specified string, because based on my statalist search that seemed the easiest way to address the previous error
Code:
 reshape long B C D E F G H I J K L M N O P, i(CountryName) j(Year, string)
This is what I get:
variable B already defined
r(110);

I also tried this code, but god another error, and tried to redress with the string specification

Code:
. reshape long B C D E F G H I J K L M N O P, i(CountryName) j(Year)
but that also didn't work:
variable Year contains all missing values
r(498);


Note, I imported this from excel, where B C F E etc were years, but stata converted them to letters. I am not sure if that is relevant.

Here is the dataex extract of my data:

Code:
* Example generated by -dataex-. For more info, type help dataex
clear
input str24 CountryName long(B C D E F G H I J K L M N O P) float id
"Afghanistan"                26433058   27100542   27722281   28394806   29185511   30117411   31161378   32269592   33370804   34413603   35383028   36296111   37171922   38041757   38928341   1
"Albania"                     2992547    2970017    2947314    2927519    2913021    2905195    2900401    2895092    2889104    2880703    2876101    2873457    2866376    2854191    2837743   2
"Algeria"                    33641007   34166976   34730604   35333882   35977451   36661438   37383899   38140135   38923688   39728020   40551398   41389174   42228415   43053054   43851043   3
"Angola"                     20149905   20905360   21695636   22514275   23356247   24220660   25107925   26015786   26941773   27884380   28842482   29816769   30809787   31825299   32866268   4
"Argentina"                  39289876   39684303   40080159   40482786   40788453   41261490   41733271   42202935   42669500   43131966   43590368   44044811   44494502   44938712   45376763   5
"Armenia"                     2958301    2932615    2907615    2888094    2877314    2876536    2884239    2897593    2912403    2925559    2936147    2944789    2951741    2957728    2963234   6
"Australia"                  20697900   20827600   21249200   21691700   22031750   22340024   22733465   23128129   23475686   23815995   24190907   24601860   24982688   25365745   25687041   7
"Azerbaijan"                  8484550    8581300    8763400    8947243    9054332    9173082    9295784    9416801    9535079    9649341    9757812    9854033    9939771   10024283   10093121   8
"Bahrain"                      958423    1035924    1114645    1185075    1240864    1278153    1299942    1315029    1336073    1371853    1425793    1494077    1569440    1641164    1701583   9
"Bangladesh"                140921154  142660381  144304164  145924795  147575433  149273134  151005733  152761413  154517385  156256287  157977151  159685421  161376713  163046173  164689383  10
"Barbados"                     277475     278701     279946     281107     282131     282987     283698     284294     284825     285327     285798     286229     286640     287021     287371  11
"Belarus"                     9604924    9560953    9527985    9504583    9483836    9461643    9446836    9443211    9448515    9461076    9469379    9458989    9438785    9419758    9379952  12
"Belize"                       291338     299031     306822     314655     322465     330236     338001     345707     353366     360926     368399     375775     383071     390351     397621  13
"Benin"                       8216893    8454790    8696915    8944713    9199254    9460829    9729254   10004594   10286839   10575962   10872072   11175192   11485035   11801151   12123198  14
"Bhutan"                       657404     664873     671611     678329     685502     693297     701582     710235     719053     727885     736706     745563     754396     763094     771612  15
"Bolivia"                     9395449    9558438    9721457    9884790   10048597   10212951   10377677   10542375   10706517   10869732   11031822   11192853   11353140   11513102   11673029  16
"Bosnia and Herzegovina"      3765422    3762791    3754261    3735945    3705478    3661173    3604972    3542598    3482106    3429362    3386263    3351534    3323929    3300998    3280815  17
"Botswana"                    1835911    1875458    1915636    1953495    1987106    2015406    2039551    2062551    2088619    2120716    2159925    2205076    2254067    2303703    2351625  18
"Brazil"                    188167353  190130445  192030362  193886505  195713637  197514541  199287292  201035904  202763744  204471759  206163056  207833825  209469320  211049519  212559409  19
"Brunei Darussalam"            370262     374967     379418     383902     388634     393687     398997     404414     409778     414914     419791     424481     428960     433296     437483  20
"Burkina Faso"               13829173   14252029   14689725   15141098   15605211   16081915   16571252   17072791   17586029   18110616   18646350   19193236   19751466   20321383   20903278  21
"Burundi"                     7607850    7862226    8126104    8397661    8675606    8958406    9245992    9540302    9844301   10160034   10488002   10827010   11175379   11530577   11890781  22
"Cape Verde"                   469171     475067     480846     486667     492644     498858     505241     511740     518276     524740     531140     537499     543764     549936     555988  23
"Cambodia"                   13477705   13679953   13883835   14093605   14312205   14541421   14780454   15026330   15274506   15521435   15766290   16009413   16249795   16486542   16718971  24
"Cameroon"                   18223677   18730283   19252674   19789922   20341236   20906392   21485267   22077300   22681853   23298376   23926549   24566070   25216261   25876387   26545864  25
"Canada"                     32571174   32889025   33247118   33628895   34004889   34339328   34714222   35082954   35437435   35702908   36109487   36545295   37065178   37593384   38005238  26
"Central African Republic"    4118075    4198004    4273368    4337623    4386765    4418639    4436411    4447945    4464171    4493171    4537683    4596023    4666375    4745179    4829764  27
"Chad"                       10457122   10818031   11183589   11560142   11952134   12360986   12784748   13220433   13663562   14110971   14561658   15016761   15477727   15946882   16425859  28
"Chile"                      16354507   16530201   16708255   16886184   17062531   17233584   17400359   17571511   17758969   17969356   18209072   18470435   18729166   18952035   19116209  29
"China"                    1311020000 1317885000 1324655000 1331260000 1337705000 1345035000 1354190000 1363240000 1371860000 1379860000 1387790000 1396215000 1402760000 1407745000 1410929362  30
"Colombia"                   43200901   43737512   44254972   44750054   45222699   45662747   46075721   46495492   46967706   47520667   48175048   48909844   49661056   50339443   50882884  31
"Comoros"                      626427     641624     657227     673251     689696     706578     723865     741511     759390     777435     795597     813890     832322     850891     869595  32
"Congo Republic"             56578046   58453687   60411195   62448572   64563853   66755151   69020749   71358804   73767445   76244532   78789130   81398765   84068092   86790568   89561404  33
"Congo, Rep."                 3745143    3876123    4011487    4145400    4273738    4394842    4510197    4622757    4736965    4856093    4980996    5110701    5244363    5380504    5518092  34
"Costa Rica"                  4345421    4404626    4463123    4520739    4577371    4633086    4688003    4742111    4795390    4847805    4899336    4949955    4999443    5047561    5094114  35
"Cote d'Ivoire"              18754914   19171250   19605568   20059147   20532944   21028652   21547188   22087506   22647672   23226148   23822726   24437475   25069226   25716554   26378275  36
"Cuba"                       11261241   11251117   11236975   11226711   11225833   11236671   11257112   11282722   11306909   11324777   11335108   11339255   11338146   11333484   11326616  37
"Djibouti"                     794554     805456     816361     827820     840194     853671     868136     883296     898707     913998     929117     944100     958923     973557     988002  38
"Dominica"                      70718      70797      70829      70848      70877      70912      70954      71019      71091      71175      71307      71460      71626      71808      71991  39
"Dominican Republic"          9218681    9338856    9458079    9576736    9695117    9813219    9930916   10048226   10165182   10281675   10397738   10513111   10627147   10738957   10847904  40
"Ecuador"                    14059379   14296554   14535740   14774412   15011114   15243885   15474099   15707473   15951832   16212022   16491116   16785356   17084359   17373657   17643060  41
"Egypt"                      76873670   78232124   79636081   81134789   82761244   84529251   86422240   88404652   90424668   92442549   94447071   96442590   98423602  100388076  102334403  42
"El Salvador"                 6079395    6105810    6131767    6157678    6183877    6210567    6237922    6266076    6295124    6325121    6356137    6388124    6420740    6453550    6486201  43
"Equatorial Guinea"            784494     821686     860839     901589     943640     986861    1031191    1076412    1122273    1168575    1215181    1262008    1308966    1355982    1402985  44
"Eritrea"                     2918209    2996540    3062782    3119920    3170437    3213969    3213969    3213969    3213969    3213969    3213969    3213969    3213969    3213969    3213969  45
"Estonia"                     1346810    1340680    1337090    1334515    1331475    1327439    1322696    1317997    1314545    1315407    1315790    1317384    1321977    1326898    1331057  46
"Eswatini"                    1036095    1042651    1049948    1057462    1064841    1072029    1079285    1086843    1095022    1104038    1113994    1124808    1136274    1148133    1160164  47
"Ethiopia"                   78489205   80674343   82916236   85233923   87639962   90139928   92726982   95385793   98094264  100835453  103603461  106399926  109224410  112078727  114963583  48
"Fiji"                         827869     836185     845356     853636     859816     863451     865065     865602     866447     868632     872406     877460     883490     889955     896444  49
"Gabon"                       1430144    1472565    1518538    1568925    1624146    1684629    1749677    1817070    1883801    1947690    2007882    2064812    2119275    2172578    2225728  50
"Gambia"                      1591444    1639846    1689288    1740277    1793199    1848142    1905020    1963708    2024037    2085860    2149134    2213900    2280092    2347696    2416664  51
"Georgia"                     3880347    3860158    3848449    3814419    3786695    3756441    3728874    3717668    3719414    3725276    3727505    3728004    3726549    3720161    3714000  52
"Ghana"                      22379057   22963946   23563832   24170943   24779614   25387713   25996454   26607641   27224480   27849203   28481947   29121464   29767108   30417858   31072945  53
"Grenada"                      104938     105183     105457     105787     106227     106786     107452     108172     108900     109603     110263     110874     111449     112002     112519  54
"Guatemala"                  13213330   13477017   13739299   14000190   14259687   14521515   14781942   15043981   15306316   15567419   15827690   16087418   16346950   16604026   16858333  55
"Guinea"                      9307421    9518159    9738796    9964470   10192168   10420459   10652032   10892821   11150970   11432096   11738434   12067516   12414292   12771246   13132792  56
"Guinea Bissau"               1377582    1411545    1446936    1483920    1522603    1562996    1604981    1648259    1692433    1737207    1782434    1828146    1874304    1920917    1967998  57
"Guyana"                       746335     746477     746815     747718     749430     752029     755388     759281     763371     767433     771363     775218     779007     782775     786559  58
"Haiti"                       9344784    9495336    9646570    9798046    9949318   10100320   10250922   10400672   10549007   10695540   10839976   10982367   11123183   11263079   11402533  59
"Honduras"                    7634295    7808520    7980955    8150780    8317467    8480670    8640692    8798524    8955579    9112904    9270794    9429016    9587523    9746115    9904608  60
"India"                    1165486291 1183209471 1200669762 1217726217 1234281163 1250287939 1265780243 1280842119 1295600768 1310152392 1324517250 1338676779 1352642283 1366417756 1380004385  61
"Indonesia"                 229318262  232374239  235469755  238620554  241834226  245115988  248451714  251805314  255128076  258383257  261556386  264650969  267670549  270625567  273523621  62
"Iran"                       70554756   71336476   72120608   72924833   73762519   74634959   75539881   76481963   77465769   78492208   79563991   80673888   81800204   82913893   83992953  63
"Iraq"                       27448124   27911242   28385739   28973157   29741977   30725305   31890012   33157061   34411949   35572269   36610632   37552789   38433604   39309789   40222503  64
"Israel"                      7053700    7180100    7308800    7485600    7623600    7765800    7910500    8059500    8215700    8380100    8546000    8713300    8882800    9054000    9216900  65
"Jamaica"                     2754414    2768229    2781869    2795839    2810464    2825932    2842128    2858710    2875137    2891024    2906242    2920848    2934853    2948277    2961161  66
"Japan"                     127854000  128001000  128063000  128047000  128070000  127833000  127629000  127445000  127276000  127141000  126994511  126785797  126529100  126264931  125836021  67
"Jordan"                      5991547    6255290    6556473    6893258    7261541    7662858    8089963    8518992    8918822    9266573    9554286    9785840    9965322   10101697   10203140  68
"Kazakhstan"                 15308085   15484192   15776938   16092822   16321872   16557202   16792090   17035551   17288285   17542806   17794055   18037776   18276452   18513673   18754440  69
"Kenya"                      37649039   38705934   39791984   40901798   42030684   43178270   44343469   45519986   46700063   47878339   49051531   50221146   51392570   52573967   53771300  70
"North Korea"                24054866   24188330   24310143   24428340   24548840   24673392   24800638   24929500   25057793   25183832   25307665   25429816   25549606   25666158   25778815  71
"South Korea"                48438292   48683638   49054708   49307835   49554112   49936638   50199853   50428893   50746659   51014947   51217803   51361911   51606633   51709098   51780579  72
"Kosovo"                      1719536    1733404    1747383    1761474    1775680    1791000    1807106    1818117    1812771    1788196    1777557    1791003    1797085    1788878    1775378  73
"Kuwait"                      2373661    2504026    2656010    2821041    2991884    3168054    3348852    3526382    3690939    3835588    3956862    4056102    4137314    4207077    4270563  74
"Kyrgyz Republic"             5218400    5268400    5318700    5383300    5447900    5514600    5607200    5719600    5835500    5956900    6079500    6198200    6322800    6456200    6591600  75
"Laos"                        5846075    5944950    6046630    6148621    6249168    6347564    6444527    6541302    6639763    6741160    6845848    6953031    7061498    7169456    7275556  76
"Lebanon"                     4759760    4767347    4764745    4813026    4953064    5202022    5537620    5913016    6261046    6532681    6714281    6819373    6859408    6855709    6825442  77
"Lesotho"                     1989933    1986926    1987130    1990135    1995575    2003793    2014988    2028528    2043448    2059011    2075041    2091532    2108327    2125267    2142252  78
"Liberia"                     3329211    3461911    3607863    3754129    3891357    4017446    4135662    4248337    4359508    4472229    4586788    4702224    4818976    4937374    5057677  79
"Libya"                       5886874    5974786    6058740    6133987    6197667    6247438    6285751    6320350    6362039    6418315    6492160    6580723    6678565    6777453    6871287  80
"Madagascar"                 18880265   19433520   19996476   20569115   21151640   21743970   22346641   22961259   23589897   24234080   24894370   25570511   26262313   26969306   27691019  81
"Malawi"                     12973693   13341808   13727899   14128161   14539609   14962118   15396010   15839287   16289550   16745305   17205253   17670193   18143215   18628749   19129955  82
"Malaysia"                   26201954   26720367   27236003   27735038   28208028   28650962   29068189   29468923   29866606   30270965   30684652   31104655   31528033   31949789   32365998  83
"Maldives"                     327489     335172     343448     353391     365730     380493     397231     415592     435018     454914     475505     496398     515704     530957     540542  84
"Mali"                       13203378   13651455   14113578   14581427   15049352   15514593   15979492   16449854   16934213   17438772   17965448   18512429   19077755   19658023   20250834  85
"Mauritania"                  3111908    3202512    3296237    3393408    3494200    3598646    3706555    3817497    3930894    4046304    4163532    4282582    4403312    4525698    4649660  86
"Mauritius"                   1233996    1239630    1244121    1247429    1250400    1252404    1255882    1258653    1260934    1262605    1263473    1264613    1265303    1265711    1265740  87
"Mexico"                    107560155  109170503  110815272  112463886  114092961  115695468  117274156  118827158  120355137  121858251  123333379  124777326  126190782  127575529  128932753  88
"Micronesia"                   105374     104442     103549     102971     102916     103448     104506     105922     107444     108886     110215     111461     112640     113811     115021  89
"Montenegro"                   615025     615875     616969     618294     619428     620079     620601     621207     621810     622159     622303     622373     622227     622028     621306  90
"Morocco"                    30804689   31163670   31536807   31929087   32343384   32781860   33241898   33715705   34192358   34663608   35126274   35581257   36029089   36471766   36910558  91
"Mozambique"                 21080108   21673319   22276596   22894718   23531567   24187500   24862673   25560752   26286192   27042001   27829930   28649007   29496009   30366043   31255435  92
"Myanmar"                    49301049   49621479   49929642   50250366   50600827   50990612   51413703   51852464   52280816   52680724   53045199   53382521   53708318   54045422   54409794  93
"Namibia"                     1971318    2006516    2043382    2081039    2118877    2156698    2194777    2233506    2273426    2314901    2358044    2402623    2448300    2494524    2540916  94
"Nepal"                      26066687   26382586   26666581   26883531   27013207   27041220   26989160   26916795   26905982   27015033   27263430   27632682   28095712   28608715   29136808  95
"New Zealand"                 4184600    4223800    4259800    4302600    4350700    4384000    4408100    4442100    4516500    4609400    4714100    4813600    4900600    4979300    5084300  96
"Nicaragua"                   5513757    5590066    5667436    5745538    5824058    5903035    5982530    6062462    6142734    6223234    6303970    6384843    6465502    6545503    6624554  97
"Niger"                      14143969   14685404   15250913   15843131   16464025   17114770   17795209   18504287   19240182   20001663   20788789   21602388   22442831   23310719   24206636  98
"Nigeria"                   142538305  146339971  150269622  154324939  158503203  162805080  167228803  171765819  176404931  181137454  185960244  190873247  195874685  200963603  206139587  99
"Macedonia"                   2040228    2043559    2046898    2050671    2055004    2058539    2061044    2064032    2067471    2070226    2072490    2074502    2076217    2076694    2072531 100
end
Thank you so much for your advice.