I have a square D service panel. One of the circuit breakers won't stay connected to the metal tab in the service panel. I've tried several new breakers, but none of them will snap onto the metal tab and stay snapped. I don't know if that particular tab is bent or worn. There is a hex screw that holds the tab in place. None of the other breakers are having this problem and all spaces are occupied. What can I do to fix the problem?