cmos resets every start-up?

[noopdoggy]

OK this is not my system, belongs to a customer. The system is 2 months old. no problems until the time change? so they say. The machine will not keep the time, and when it starts up says cmos error press f1 to continue. otherwise the system functions normally.. even if you go and change the date/time in the bios, it won't stay. We have changed the mb battery, no luck. millenium won't set a back up because it lists the date as 1899!...
800 mz duron
win ME

any thoughts on what is causing this or how the cure it?

PS Thanks for curing my win XP/Direcpc problem...Way to Go!