What gives you the error
The inverter
Or something in the TT ?
Also sound like you are using a back feed , suicide cord system
Since you said plugged into one of the Tt outlets
Since you are using one outlet
Try turning off all the the other circuit breakers
Then turn them on one at a time, see which circuit created the fault
My best guess would be fridge or water heater
Something with a heating element shorting out
I assume, you already turned off the converter
You could also check the breaker panel
Maybe somebody bonded the neutral to ground and the inverter don't like that