I’m using Stata 15.0 to analyse a quarterly panel data. I am using xtmixed command to perform a random coefficients specification. My dependent variable is (dep) and I have five independent variables(v1:v5). I want to calculate the fixed effect and the random effects of one of the independent variables (v3) as in :

Cooper, M. J., Knott, A. M., & Yang, W. (2019). RQ innovation efficiency and firm value. Retrieved from https://papers.ssrn.com/sol3/papers....act_id=2631655

I want to run the model using 40-quarter rolling windows. I also require all firms to have a minimum of six quarters of non-missing (v3). I’m using the following command:

Code:
rolling, window(40) clear keep(qdate): xtmixed dep v1 v2 v3 v4 v5 if rd2_count >= 6 || gvkey: v3, covariance(unstructured)
But when I use the predict command to get the best linear unbiased predictions of the random coefficient

Code:
 predict re, reffects
I get the error:

last estimates not found r(301).

Is there another command that I can use to achieve my target??

My dataex:

Code:
* Example generated by -dataex-. To install: ssc install dataex
clear
input long gvkey int qdate double rd_count float(dep v1 v2 v3 v4 v5)
1013 125  1 4.2810454   3.89506   .8870679  1.7791808   .5732369 -.09266371
1013 126  1 4.3009386   3.99765   .8870679  1.8234196   .8127064 -.09266371
1013 127  2 4.3155127  4.057127   .8870679  2.0518134  4.1086745 -.09266371
1013 128  2 4.1705956  4.060029   .8342126  2.0429072 -.08229524 -.04186421
1013 129  2  4.367281  4.044962   .8342126  2.0203547   .4631049 -.04186421
1013 130  2 4.4289937  4.053418   .8342126  2.1414769  -.9063404 -.04186421
1013 131  3 4.4893775 4.0594945   .8342126  2.1458142   4.390131 -.04186421
1013 132  3  4.364982 4.0491204    .900974  2.1057184  2.2903101  .06859277
1013 133  3  4.488625 4.0766726    .900974  2.1660779  2.5427036  .06859277
1013 134  3  4.536313 4.1267147    .900974  2.2160463   2.738644  .06859277
1013 135  3   4.65515 4.1411643    .900974   2.298075    3.05386  .06859277
1013 136  3 4.5127916 4.1207595   .9722929   2.255179   2.982191  .27345634
1013 137  3 4.7324457  4.161193   .9722929  2.3303947  2.9310336  .27345634
1013 138  4  4.750897   4.15721   .9722929  2.3105533   3.132228  .27345634
1013 139  3  4.854356  4.191653   .9722929   2.405954   3.155254  .27345634
1013 140  3  4.802167  4.196976  1.0932647   2.398168    3.06269          0
1013 141  3  4.944082 4.2664194  1.0932647   2.505281   3.219236          0
1013 142  4  5.013658 4.3102756  1.0932647   2.526928   3.602395          0
1013 143  3  5.157053  4.365465  1.0932647   2.580898   3.548755          0
1013 144  3  5.091238  4.457482  1.5303947   2.580898   3.815798          0
1013 145  3  5.262965 4.6495795  1.5303947  2.7686434   3.664126          0
1013 146  3  5.381339  4.772767  1.5303947  2.7851346   3.638165          0
1013 147  3  5.541468  4.875808  1.5303947   3.049842   3.401331          0
1013 152  2  5.657375  5.419238  2.0834336  3.3364456  3.8731575          0
1013 153  2   5.81304  5.481526  2.0834336    3.41464   3.590853          0
1013 154  2  5.893013  5.507131  2.0834336   3.378918  3.8895116          0
1013 155  1  5.981795  5.548924  2.0834336    3.54887   5.209546          0
1013 158  1  6.281796  5.686168  2.5994995   3.577249  4.1402097          0
1013 159  1  6.452207  5.743215  2.5994995   3.529327   3.329415          0
1013 161  1   6.64717  5.950989  3.1113796   3.628944   3.586653          0
1013 162  1  6.792793  6.207435  3.1113796  4.2044387   2.513656          0
1013 163  1  6.939254  6.411161  3.1113796   4.248495   3.201363          0
1013 164  1  6.698638  6.525909  2.4884005  4.3201513  2.8803215          0
1013 166  2  6.305362  6.598645  2.4884005  4.4308167   3.008747          0
1013 169  2    5.6981  6.293049  2.0281482  4.4379344   3.769076          0
1013 170  3  5.460011  5.764878  2.0281482  4.2282925   3.445852          0
1013 171  2  5.397257  5.331752  2.0281482  3.9512436   4.451891          0
1013 172  2  5.270946  5.250701   1.740466   3.802208   4.318914          0
1013 174  5  4.865995  5.332236   1.740466   3.962716   3.606611          0
1013 175  5  5.040194  5.259057   1.740466   3.505557   4.344455          0
1013 176  5  4.917789  5.207846   2.014903  3.4111476   4.301792          0
1013 177  5  4.999237  5.133443   2.014903  1.7227666   5.101518          0
1013 178  5  5.415656   5.48272   2.014903   2.397895  4.7272463          0
1013 179  4  5.574053  5.451038   2.014903   2.564949   4.603699          0
1013 180  4  5.484797  5.433722   2.104134  2.5176964   4.806886          0
1013 181  3  5.665734  5.389072   2.104134  2.6602595  4.6038895          0
1013 182  3  5.722277  5.381279   2.104134  2.8033605     4.8722          0
1013 184  3  5.608739  5.384953  2.1517622   2.721295  4.6136045          0
1013 185  3  5.880812  5.355642  2.1517622  2.9014215    4.46041          0
1013 186  4  5.839478  5.348535  2.1517622   2.912351   4.475927          0
1013 187  5   5.72815    5.3303  2.1517622   2.985682  4.4580727          0
1013 189  5  5.856217   5.31959  2.2027647   2.944439   4.525185          0
1013 190  5  5.846728  5.307773  2.2027647   2.850706   4.539351          0
1013 191  5  5.797576  5.294309  2.2027647  2.8390784  4.4781775          0
1013 193  3  5.974319  5.311727   2.360854   2.873565    4.64183          0
1013 194  3  5.944897   5.30231   2.360854   2.867899   4.646504          0
1013 195  3  5.864483  5.176714   2.360854   2.862201  4.6769137          0
1013 196  4  5.538515  5.131672  2.2027647  2.9704144   4.528624          0
1013 197  4  5.617135  5.129307  2.2027647    3.08191  4.5467887          0
1013 199  4  5.581991  5.064492  2.2300143   3.020425  4.4652066          0
1013 200  4  5.613128  5.035653  2.2300143   2.944439   4.494406          0
1013 201  4  5.718343  4.996536  2.2300143   2.912351   4.510057          0
1013 202  4  5.744925  4.987025  2.2300143   2.850706   4.505825          0
1017 121  8 3.5195136 3.6580336   .3442987  -.3523984   4.920324          0
1017 122  7  3.664126  3.724464   .3442987  -.3667253    4.92923          0
1017 123  8  3.529004 3.7695835   .3442987  -.6180397   5.177826          0
1017 124  9  3.621082  3.772416   .3442987  -.8074363   5.384064          0
1017 125  5  3.771427  3.765979  .26849926 -1.1332037   5.002959          0
1017 126  7  3.489727  3.752183  .26849926  -.7465479   4.897459          0
1017 127  9  3.514615  3.767483  .26849926  -.7011794   5.380409          0
1017 128  7 3.4108176  3.753379  .26849926 -1.1551826   5.442413          0
1017 129  7  3.317743  3.754269  .24451357 -1.0300195   4.794981          0
1017 130  6 3.2007525  3.767136  .24451357  -.7381446   4.924206          0
1017 131 10  3.345262 3.7840986  .24451357  -.6635884   5.313014          0
1017 132  7  3.495992  3.794972  .24451357  -.9364935   5.501009          0
1017 133  9 3.4349544 3.8059065  .15014265 -1.1086626    4.89318          0
1017 134  9   3.32338  3.805684  .15014265   -.424648  4.4932103          0
1017 135 11  3.313859  3.805239  .15014265 -.25231493     5.2781          0
1017 136  7  3.633763  3.791504  .15014265  -.3011051   5.425611          0
1017 137  6  3.426735 3.7845304   .0971267  -.9038682   5.427823          0
1017 138  8  3.431112  3.771427   .0971267  -.5816058  4.5213647          0
1017 140  6 3.5296786  3.752769   .0971267  -.5430046   5.546708          0
1021 120  4 2.5020096  1.911023 -1.1647521  -.7465479   1.255046  -2.063568
1021 121  4  2.592265  1.909098 -1.1647521 -1.0078579  1.4424384  -2.063568
1021 122  4 2.1637826 1.8908504 -1.4271164   -.236989  1.1546775  -2.995732
1021 123  6 2.2748027  1.866403 -1.4271164 -.58519006    1.96375  -2.995732
1021 124  5 2.2451677  1.836414 -1.4271164  -.6635884   1.595339  -2.995732
1021 125  5   2.31836  1.817427 -1.4271164 -1.0300195  1.7358943  -2.995732
1021 126  5 2.1804175  1.790759 -1.5847453  -.9088187  1.6605113  -2.886878
1021 127  5  2.248129 1.7662708 -1.5847453  -.9339457  1.9384538  -2.886878
1021 128  5 2.3179662 1.7430943 -1.5847453 -1.1551826  2.0020204  -2.886878
1021 129  5  2.280646 1.7518052 -1.5847453 -1.0642109  1.9844438  -2.886878
1021 130  4  2.237086 1.7313015 -1.5141277 -1.0847094  2.0352283          0
1021 131  5 2.2982757 1.7072903 -1.5141277  -.8370175  2.0547645          0
1021 132  . 2.2749054 1.7034745 -1.5141277   -.796288   2.091123          0
1021 133  5  2.219964 1.3658365 -1.5141277  -.4812669  2.0059295          0
1021 134  6  2.144761 1.3519617 -1.7778566   -.549913  2.0649621          0
1021 139  4 1.8691834 -.4764242  -1.826351 -1.2801342  1.9533113          0
1021 140  5   1.94976 -.5905906  -1.826351 -1.3318062  1.9444805          0
1021 141  4 1.9074663 -.5798185  -1.826351 -1.5945493  1.8944665          0
end
format %tq qdate
label var rd_count "count of rd"