> [...] I get a data file with a name like SCBEDF~1.DAT [...]
I have never seen anything like this and don't know what could cause this. My guess would be some permissions issue or an access violation (e.g. the data file Inquisit is trying to write to is already opened or locked by a different application).
As for the (perhaps) missing demographics data: Check whether it has been appended to any of the demographics data files that already existed. Unless /separatefiles=true is specified, Inquisit will append data to existing files.
P.S.: Your post suggests you are using Inquisit 4. If so, you should post to the correct forum section in the future (you posted in the Inquisit 3 section).