When calling HP for this, double-check the part number of the system board if it does turn out the board needs replacing, and make sure you note which one is which (after double-checking the CPU #2 installation).
Having to call HP recently for one with the older latch-type, the HP phone operator and first supervisor seemed insistent the server we had was a screw-down type and didn't even bother consulting their own advisory notice it seems (the one that tells you how to figure out the board/heatsink type without opening it up).