When starting my Xen kernel in Ubuntu or openSUSE, the following text appears a lot and generally won't allow me to boot under xen:

Time went backwards (useless numbers counting upwards in hex)

I looked up this but couldn't find a cure.

My processor is AMD Athlon X2 4800+ (2.5GHz) with AMD-V support, virtualisation enabled in bios. (would bios upgrade help with that?)