A couple days ago, i was having some big problems.
Some applications would work, others wouldn't, and the system clock was wrong.
Eventually i got an error message saying:

CMOS/GPNV Checksum Bad

Googling on this, it appeared that I had a bad CMOS battery.
So i replaced it.
For a day after that, everything was fine.
Today, the system clock is wrong again.
Nothing else is wrong, all apps are working.

When i reset the clock, i get this message (in a dlg box)

Sound server fatal error:
cpu overload, aborting

but the clock and calender do get set.

I'm trying to think of what could be wrong.
1. I replaced a battery that wasn't the CMOS battery.
Is there more than one battery on a motherboard?

2. There is a hw problem such that it drains the CMOS battery very quickly.
If so, what?

3. something else
Any ideas?

Check out this link.

thanks.

today it started up with no error message.

reading the link you gave, it lists power surges and lightning.
i get a lot of those.
even though its on a APS backup/surge protector, maybe it still has an effect.
or i have a bad rtc.
is there a test that can be performed for the rtc?

You can check your log messages (for lost ticks and the like), and troubleshoot your mobo. I've never had an rtc failure.