[cem] Stata cem r(3301)

Dear CEM List, I am attempting to run cem in Stata MP 14: cem months (#15) if laac_none_base50p!=., treatment(laac_none_base50p) show I get the following error: cemStata(): 3301 subscript invalid <istmt>: - function returned error r(3301); My data: 479,808 observations months ranges from 1-156 and is a real number laac_none_base50p is either 0 (n=1,140) or 1 (n=472,312) Please help; I can't find any support for this error. Andrew