>>I created two .EXE files. One appfile.exe without Debug and another one appfile_deb.exe, with Debug. Placed them both on the customer server. The main user has appfile.exe on her desktop. But she decided to take a day off today; so I won't find out till Monday. And if she still has a problem, I will ask her to start the application with the appfile_deb.exe. So, hopefully I will find out, next week, the cause of the problem or at least the line number.
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>And how much larger is the other one?

The size difference does depend on the contents of the APP/EXE file. From what I'd seen, enabling debug information generally doesn't affect report and label forms (since they usually don't contain program code), but PRG and screen forms are affected. I've seen EXE/APP balloon to twice the size when debug information is enabled (if I'm not mistaken, an EXE generated from VFP is essentially an APP, which consists of the p-code, bundled with vfpXrun.exe - where X corresponds to the version of VFP used).