A checksum error is generated when the CMOS information present after the POST (Power On Self Test) does not match the settings at the previous shutdown.
Are you powering down your PC properly?
Replace the battery and perhaps reset the CMOS using the reset jumper on Motherboard. The RTC (Real Time Clock) error is indicitive of a bad battery....yeah, try that first.
Hope this helps.
[SIZE=\"1\"]E6400 @ 3.4 , Noctua 120
7900GT @ 670/1680 , VF900
2 x 1GB Patriot 6400 @ 425
WD SATA 250GB
Neo HE 550
P180 / G15 / MX1000[/SIZE]