Same reason some boards can't support Core Duo 2. The board might of been put out of production before they were released so no bios was ever made that supported the chip. Or there could be some other factor that could cause incompatability. I don't know the differences in those processor right off. However, it'd probably be about as cheap to just get a new motherboard and newer processor instead of rather old ones such as the 5xx and 6xx series.