Never use compression, all sorts of weird errors can occur. If it's on turn it off, after decompressing all files.
Set the apps as read only and see what is running when the attempt to write to a read only file occurs.
Is the virus scanner corrupting the files?
Is the HDD on the way out. Run a scan disk to check.
Is there a trojan active.
Does the server have bad memory.
Does the HDD have bad cache ram chips.

What O/S, networking topology and version of VFP and you using

>First of all, I'd like to thank all of you for your suggestions. Anyway, I thought all of you would like an update on the situation.
>
>It seems that there is something on the customer's server that is periodically modifying files. After the software is installed it works OK for a few hours. After a period of a few hours, the program will start to error out on random modules -- not necessarily on portions that use ActiveX components (found this out later on -- the first module reported was one that used several activex components). If the entire application folder from the server is copied to a local drive, the copy will exhibit same error. Replacing the .APP files (our application is partitioned into .APP files rather than a monolithic .EXE to allow modules to be replaced) with a "fresh" copy would "correct" the problem (at least until something modifies it again). As for what exactly is modifying the contents I've no idea (perhaps file compression gone bad? Had that happen once before on our Novell server because a misconfiguration of the memory manager -- the files would get compressed, but the on-the-fly
>decompress would fail because it couldn't load the module).