Bogart: Can you test with a multimeter if the compound is conducting? I don't see any screw heads in contact with anything else in your pictures.
Measuring with a meter on the 20Mohm range, it does not appear to be conductive. Neither your silver compound, nor the white stuff I added.
I think it's the screw head thing. This image (of the #2 board) shows how the one screw head cut through the insulating layer on the top side of the PCB and made contract with the top plane:
http://i.imgur.com/fHBsNqo.jpg