Illegal Sumout error, but why?

I'm seriously in the dark at the minute. My overclock was instable a week or so ago, I then upped the voltage of my CPU and then I no longer received the ILLEGAL SUMOUT errors when running blend test. The illegal sumout errors occur during the 896K test as far as I know. Every single time so far it has failed on that stage of the blend test.

Now I have not changed ANYTHING in the bios since then and now I am receiving the errors again. (Again on the 896K test) IntelBurnTest runs 15 tests with 1500MB ram no problem. HCI Memtest 2x 1024 MB runs for over 250% no errors. Changing PL from 7 to 13 does not fix the problem either, and upping NB voltage to 1.45V didnt even fix the problem for me. FSB termination voltage I havent tried yet, but it used to be stable on 1.20V for me and now at 1.33V it still is giving errors so...

My brain is going to explode...

run small test to make sure it is the cpu, as blend is stressing all three cpu/nb/ram. if cpu passes use large which is strictly for ram. if large passes and since blend is failing that means the NB needs more voltage.

when all else fails go back to stock, run the same tests. if they pass, then start oc process agian.

Which thread(s) are failing? It may be time to tweak your GTL reference voltages.

Ok I'll try Small FFT, but doesnt IntelBurnTest stress the CPU even more and shouldnt that be detecting errors if the processor is not getting enough juice?

I'll try Orthos Blend tonight and OCCT CPU tomorrow. Currently running Small FFT now.

Prime95 Small FFT ran for 11 hours and 30 minutes without errors. Going to try Orthos Blend tomorrow.