>Is it possible that the app was complied under a different version of VFP than the one he has installed with runtime Setup?

Yep, but this woulnd't be a sudden change, I don't think. Also, its his development machine, whereever the VFP Tool is installed, the runtime is probably installed too? So, if he recompiled in an old VFP, he would probably still have the old runtimes.

But its still a possiblility.