I have an AMD SMP system and have been able to run the beta with 2 non-service clients and with 2 service clients, and a mixture of DF and on DF clients at the same time. I now run as a service so I haven't tried two non-service runs of the client on the latest beta.
This is an obvious thing but I thought I would ask just in case. Do you the DF beta client installed in two seperate directories and are running the two instances of the clients from those two seperate directories?
I can't remember if you said this or not, but did you run memtest86 on your Dual box and get a clean bill of health?
Have you also tried deleting both directories, re-installing the latest NON-beta client in both directories, then copying the files in the latest beta client into those directories and starting fresh?
Jeff.