This has been an ongoing problem in both v8 and 9, but it's only intermittent. Generally we restore the project from backup, or if it's a new one that broke we just delete the project files and recreate it by including main.prg and recompiling.

It hasn't happened since we turned off oplocks and caching on all our machines...I guess what's been happening is that any kind of fault that prevents the project files on disk from being actually updated with the real project contents ends up making the project files invalid - disabling caching seems to solve most FoxPro corruption issues (not just projects, but shared data files etc).

HTH, Matt.