As a trouble shooting test, I would jumper out that IG right at the place where the IG lands on the equipment end (connected to the EGC coming in with the supply) basically just eliminating the "isolated" part. IBM figured out in the early 80s that IG can cause more problems than it fixes, particularly if it is not connected right to the MBJ.
We ended up removing it from our recommendations.

Greg Fretwell