[Zope] Database error: File can't be locked

For no apparent reason yesterday we started getting a 'Serious Application Error' when starting Zope. In the PCGI.LOG we see: "Database error: File can't be locked." Normally this means someone else is using the file, but we don't know which file it's talking about. Shutting down and restarting Zope doesn't unlock the file and doesn't solve the problem. Any idea what the problem is or how to solve it? Or even which file it's talking about? Thanks, Alan Alan Johnston DevIS (Development InfoStructure) adjohnston@worldnet.att.net 919-844-4124