Bob,
We had this happen under the DiamondShield that was on the cap over the windshield. It looks like mold under the film caused, we were told, by a bad adhesive that was used.
I set up scaffolding and spent two days picking the stuff off. I heated it up with a hair dryer and then went to work using plastic scrapers to get underneath it. I had hoped that it would come off in a sheet but not so. If you google it, you will find many ideas on what has worked for others. I can tell you that I tried Xylene and it did not work. Rubbing alcohol did not work. The only thing that worked for me was the heat. I then cleaned off the leftover adhesive with Xylene and put a good coat of wax on it.
George