Hi Mark,
It is difficult to diagnose what is happening without knowing where the error is happening.
If it is possible for you to provision a site for me on Rackspace for a test environment, then I could deploy a debug build and possibly get a stack trace when an error happens. Or by trial and error I could try adding logging statements here and there in places or disabling things that might be problem spots for their environment to gather clues.
I can't promise that this will make it possible for me to find the problem or a solution, but I am willing to try.
Best,
Joe