The “Project xyz is busy. Retrying…” status during send/receive means that the repository on the send/receive server is locked.
Normally this lock is released quickly, but if a user gets an error that prevents the final unlock command from being sent, the project will stay locked for about 30 minutes. We were trying to give plenty of time for a slow connection. I have thought we may be able to shorten that time if we reset the start time for the lock whenever a step during the send/receive is processed.
When the project is locked, no user will be able to do send/receive - even the user that had the lock originally. We did this since some users have more than one machine.
John+Wickberg
Paratext Support