>I did create a new project. The build still failed. I then tried to rebuild a second project. It failed in the same way: the last thing I saw was rebuilding type libraries then the message "File is not open" I've now reinstalled VFP and still have the same problem :-( Registry problem maybe?

One thing to check is your new backup software - maybe, for some reason, it meddles with some of Fox's extensions. Try to open your classlibs and forms as tables, just to make sure they're complete.

Also, "File is not open" is supposed to mean the connection to a file was lost while the file was open - be it a file on a network and the network goes down (or just the machine the file was on, or your wireless acts up, or it's on a mapped drive which is suddenly unmapped), or on a removable medium, or the OS just decided to close the file on you (some versions of Windows used to do that - IIRC, combination of W2000 workstation and files on a W98 machine).