Probably not enough voltage or heat. Are you using a stock heatsink and what are your temps?. Edit, Just looked at your cooler. What temps are you getting?
Try this. Go into the bios and disable Turbo and Cool & quiet. Manually set the voltage to 1.425 and set the CPU X to 19 and save and exit and see what happens. Just keep a eye on your temp. If its stable, then try your CPU X at 19.5