BlockedIndefinitelyOnMVar exception

Hi, I have a very big and highly threaded program that generates a BlockedIndefinitelyOnMVar exception when run. I have spent a reasonable amount of time pouring over the source code, as has Max Bolingbroke. Neither of us have the slightest idea why it raises the exception. Some questions: * Does anyone know the exact sequence of actions that causes this exception to be thrown? I couldn't find it written down. * How confident are people that this exception does really mean that it is in a blocked state? Is there any chance the error could be raised incorrectly? * Any debugging tips for this problem? Thanks, Neil