Stability issue (Prime 95)

Have a system a little less than a month old, and the goriest details I would assume would possibly be of use:
Am2 3500+
Crosshair
2x 1GB OCz DDR2 667 (4-4-4-12) in dual channel
OCz GameStream 600w

The 3500+ has a Big Typhoon on it. I sanded the Typhoon myself w/ 400 and then 600 grit waterproof sandpaper. Used AS5. Troweled the AS5 out of habit (my previous CPUs were Socket A), despite AS recommendation to use a rice kernel size drop and just smoosh it and because I wasn't sure I'd be able to get it spread evenly the recommended way because the Crosshair leaves very little space for moving the HSF assebly around in between its massive chipset heatpipe coolers.

According to Everest:
CPU Idle temp: 34-35*c
CPU load temp 39 - 40*c

At factory settings, I have run Prime 95 twice, once a little over a week ago, and once last night.

1st run:
4 hours:
FATAL ERROR: Rounding was 0.4609375, expected less than 0.4

2nd run:
8 1/2 hours:
FATAL ERROR: Rounding was 0.4921875, expected less than 0.4

What might be causing the instability?

possibly the RAM with an unstable timing or maybe faulty.

Try running Memtest.

Will do. RAM was audodetected 4-4-4-15, 2T. I manually set 4-4-4-12, 1T

Ran memtest for 14 hours, no errors.

what temp is the northbridge?

Under load, it is liek 40*c or so.

Switch your ram back to 2T and run Prime again.

Also have you run SuperPi at 1M? Because if it is failing it would be easier to diagnose the issue with something that doesn't take 4 hours to show the error.

I would also make sure your HTT voltage is right.

Haven't touched any voltage settings since I first powered it on about a month ago, but I'll see if I can find the proper HT votage.

SuperPi 1M runs though fine, about 38 seconds. After that, I set RAM to 2T, gonna do another Prime95 run.

Prime 95 errored out after only 45 minutes at 2T. Switching back to 1T.