Thermo-Ply should never be placed on the exterior side of fiberglass or similar insulation, because it traps moisture. Even with a well ventilated attic, moisture will form. Products like thermo ply can trap moisture. Following questions:
1. Why do you need the thermo-ply? If installed correctly, standard insulation should be sufficient.
2. If installed, thermoply should be flush against the attic side of the wall, with unfaced fiberglass insulation placed on the attic facing side of the foam board.
Remove the thermo ply since it was installed incorrectly. If it has moisture stains, throw it away (mold can build up on it). If you feel that you need more protection from heat on this wall, do the following:
seal all air penetrations on the attic side of wall (drywall seams, electrical and plumbing holes in drywall, etc) to prevent hot air from crossing the drywall.
ensure that the fiberglass batts were installed correctly. Batts should fully encapsulate the opening between the studs. If you are not proficient with insualtion, hire an insualtion contractor to remove the foam board and examine the batt insulation. If the batts have become wet, they will need to be replaced. Ask the contractor what he feels the best insulation options are. Fiberglass, rock wool and other base products can be blown into bags which (blown in bags) provide more R value and more thorough coverage in the wall cavity.
In any case, this will not be a costly project.