That looks very simple and should be easy to spot a problem. As Stlbeer suggested, a pic showing all the terminals will help greatly.
Is your feed L1, L2 and equipment ground? It looks like you are tied to black and green to supply power to the pid. I would power the pid at 240v from black and white because a gfi upstream may not like the pid current to ground. I doubt that is the reason for your problem though.