Dear statalisters,

After having used other people's questions on the forum a lot during my research, I am now coming across an issue that has not been posted about so I am forced to ask a question myself. Would be awesome if you knew the answer!
The problem is the following. I am using an 2SLS regression on a panel dataset with currently 406 variables. I am using Stata 15.1 on Windows 10 and I ran the following code:

Code:
xtivreg DIYper1000_totaldrugs (perc_unempl_totalpeopl = yr1_NL_comp_total), vce(cluster corop_code) first
This however, returns the following error:
Code:
 variable __000012 not found
r(111);
The problem is, I do not have a variable called "__000012" in my dataset. I therefore think Stata is referring to some temporarily created variable. The problem is, I do not know how to fix this.

Another striking thing is that the regression using fixed effects does work and gives normal results

Code:
xtivreg DIYper1000_totaldrugs (perc_unempl_totalpeopl = yr1_NL_comp_total), fe vce(cluster corop_code) first
Hope my question is clear enough and you can help me out,

Kind regards,

Sophie