New home and requested to be repaired by inspector before home sales.

There probably is no equipment ground conductor to the outlet, probably missing in the wiring.

Having a GFI with no equipment ground is allowed by Code, it must be labeled "No Equipment Ground".

Have an electrician check the wiring, can provide a price to upgrade, or convince the inspector that what is there is legal.

If it is an open gound conductor, that means your green or bare wire has become disconnected from the receptacle or possibly in a junction box between the plug and the panel. Open not connected, so some how the meter cannot read from the ground prong of the receptacle to the panel. Probably the wire in the outlet box came off the ground screw or the joint came lose.