Hypertransport sync flood error

i have this error every time i try to start Mythbuntu. This hasn't happened ever since i built the computer (mid april 09) and is currently running Windows 7 (also had Kubuntu 9.04 before putting Mythbuntu)

specs:
AMD Phenom II X4 810
ASUS M4A78-E
Crucial DDR2-800 CL6 (4x2GB)
Sapphire 4870 1GB
Corsair 650TX
Hauppauge 2250

Anyone have any thoughts or ideas as to why this keeps happening?

EDIT: this only happens in mythbuntu, the system is perfectly stable in everything else (prime95, memtest, never had this problem ever)