That's pretty strange... Could you take a pic of the bottom under the cpu where the clamp goes? Something is causing the cpu to fault, it looks to me like the heat sink had decent contact. You can try just setting the heatsink on the chip and running it without the xclamp just to see if it overheats still. You may need to hold the board in your hand so the heatsink legs on the bottom are not touching a surface and lifting the heatsink off of the chip