Just ran the electricty to a used hot tub that I bought. When I turn on the control pak (Onyx Reliance Plus Control Pak) it keeps tripping the GFI, checked all the wiring and everything is connected correctly. If I take out the neutral wire then it doesn't trip, but it only gets power to one side of the relay. Is there a safety swith somewhere that I don't know about or does the hot tub need to be set-up completely w/water before it will work?

Did you run the neutral to the breaker, or the neutral bar?

Look closely on the breaker. In addition to the neutral pigtail, there is an additional terminal for the neutral. The pigtail goes to the neutral bar, and the neutral goes to the neutral terminal on the breaker. If you wire the neutral to the neutral bar, the GFCI will trip instantly.

everytime I connect the neutral to the breaker is when it trips. If I take the neutral out then I get power to only one side of the relay. Does the pump, blower and all the hoses have to be connected to the control box so the breaker doesn't trip?

Can you post some pic's of the sub-panel wiring, as well as the wires being hooked up to the control box?