Here's the history:
I had setup a new install of Windows XP with SP2 on an Intel Core 2 Dual 6600 (2.4ghz) system. I installed client 5.10.20 to run as a service, no interaction with the desktop. I attached the client to BAM and then from the client connected to WCG. The system processes for a while. A couple days later the boinc client had unloaded itself / crashed.
Looking at the logs it seems that BAM told the client to detach from WCG which the client did but then continues to try and cruch a work unit which is probably what lead to the crash.
I've attached the two log files which had data in them. I didn't have any debug options enabled, sorry.