I've encountered this situation and discovered a problem ...

I had VFP5 installed and tried to install VFP6 to a different directory. I soon noticed a resource error message when trying to run any VFP5 compiled exe. After uninstalling VFP6, the problem was still evident. I checked the registry and it looked fine. Apparently the problem lies in the system related dll files. VFP6 will replace some but not all of the VFP5 dlls during install. After deleting the all the VFP*.DLL files from my windows/system directory, I reinstalled VFP5. Now VFP5 exes run fine.