code 124 when overclocking is vcore or less likely qpi I would say your core voltage is too low for that overclock anyhow seems low to me ( I could be wrong as I don't have sandy bridge I have a 930) could also be qpiv but I don't think that is the case with sandy bridge chips as the qpi cannot be overclocked
Do you have LLC enabled?
124 is like 99.999% of the CPU related
Here is a reference list ( thanks to GfhTattoo ):
0x101 = increase vcore
0x124 = increase/decrease vcore or QPI/VTT...have to test to see which one it is
0x0A = unstable RAM/IMC, increase QPI first, if that doesn't work increase vcore
0x1E = increase vcore
0x3B = increase vcore
0xD1 = QPI/VTT, increase/decrease as necessary
0x9C = QPI/VTT most likely, but increasing vcore has helped in some instances
0x50 = RAM timings/Frequency or uncore multi unstable, increase RAM voltage or adjust QPI/VTT, or lower uncore if you're higher than 2x
0x116 = Low IOH (NB) voltage, GPU issue (most common when running multi-GPU/overclocking GPU)
0X109 = Not enough or too Much memory voltage