>I would do that, but the problem is I have not been able to reproduce the error myself. It happens sporadically in the production environment while running the exe. As a result, I try to capture as much info as possible in the error routine to try to figure out what is happening. When I check the aliases in the data environment, it's there, but the code blows up when the alias is SELECTED.

Just and idea to try to workaround

IF NOT USED("Tmpsumm")
  SET DATASESSION TO Thisform.DataSessionId 
ENDIF
SELECT Tmpsumm

Maybe somehow it will switch to the proper datasession or give you some additional info.