installing a hot tub 50amp gfi breaker - - unit works well except when i hook up ground at controll panel at hot tub - - any ideas thanks

A common problem that occurs when hooking up a new GFCI to a spa is that the neutral and the ground get tied together at the house circuit breaker, see if this is the case and try to separate them. Please note that an electrician who wires homes often is the cause of this due to not knowing these things need to be separated for tubs. Provided that is not the case then you need to unplug all the components from the control box and disconnect BOTH wires connected to the heating element, you should be able to activate the system like this and begin plugging components in one at a time to locate your problem component.