metareg command in stata 12

I'm relatively new to stata and I'm running a meta-analysis of proportions in STATA 12 SE and then, doing a metaregression by the following commands:
1. metaprop var2 var3, random cimethod(exact): which generates _ES (effect size) and _seES (standard error of effect size) for the next command
2. metareg _ES var4, wsse(_seES)
but, the software shows the following message and it doesn't do the meta-regression:
"<istmt>: 3499 _coef_table() not found"
My meta-analysis packages are all up-to-date. (I'm using STATA 12 SE though)
Does anyone know what the problem is and how to solve it?