>I suddenly started receiving the message "Source not available" for a .prg when stepping through executing code.
>
>To make sure I wasn't having a version conflict or anything like that, I created several .prgs, each with a unique name, placed each in a separate subdirectory that participates in the project and modified some code to call each prg in turn. Each executed, but the the source was not available.
>
>I'm totally stymied--I've never had this problem before. Any ideas?
>The only thing that changed on my system was that last night I installed Diskeeper and ran it to defrag my hard drive, but I doubt that could have affected anything. I am seeing the source for classlib methods.

VFP caches code. At some point, after some extensive debugging (specially if you cancelled or selected debug/fix in debugger's menu), the debugger will get out of sync with the current version of the source - at least you're notified about that. In VFP5 I was seeing sometimes the previous version of source while the line pointer was going by new line numbers, so it seemed to execute comments sometimes. Sometimes debugger may keep a .fxp open and you wouldn't be able to recompile a .prg, for the same reasons.

You may try clearing everything - clear all, release all, clear program - but if it doesn't help, simply quit and restart Fox.
I don't know if I saw this in VFP7, though, it seems to be better with this.