The antivirus didn't make a difference... at the time this happened, it happened to not be running.
Chkdsk showed no errors.

>>I am routinely getting corruption of a vcx. To clarify, when I say corruption, what I mean is that the vcx has been completely overwritten, as if it was an empty vcx with one form class in it. Previously it had one 'custom' class with many methods in it.
>>
>>This is vfp 9. I recently reinstalled vfp 9 after a HD crash. Haven't installed any SP's yet. Is that a known problem?
>>
>>My workflow is simple: modify class, run app, exit app, modify again. Several days in a row now when I execute modify class after running the app, the vcx is blown away, i.e. it opens up as an empty form class.
>
>- Try running for a while with antivirus real-time scanning disabled
>
>- Check the condition of your computer's file system with CHKDSK