>I've a client that uses my vfp6 application in a win98se os.
>Yesterday after a system crash (caused by an email based application) the message "my.exe is not an object file" start appear and my application doesn't start any more.
>I've tryed a reinstall, delete files manually, reinstall vfp libs...I don't know!!
>Is it a Virus, operating system error??

Hard to tell from this information, but you could try the following to narrow the source of the problem.

1. To discard a general OS problem, like a virus: do the rest of the EXEs in the PC run ok? (i.e.: Notepad, Word, ...)

2. To discard a VFP runtime problem: if you build (in another PC) a dummy EXE with a single PRG like: MESSAGEBOX("Hello"), does it run?

3. If both went ok, the problem is inside your app or in something it calls...

Hope this helps you to "get near".. then you can really start looking for the problem.
Regards
Jose.