>Should I install Servicepack 4? If I do so, what could happen, if one of our customers, who has SP3 runs an EXE, that I compiled with SP4?

I am going to take the opposite view of Erik. I am appling the patch when convenient over the next 2 months. My worry is that if I don't apply the patch when I have a choice, that a software update with Windows (or something) could break and then I am forced to apply the patch in an emergency situation. I would rather to do this on my own terms.

Mixing the service packs between the VFP and application EXEs is playing with fire IMHO.