Problem Removing the AC Shroud

I'd suspect some sort of thread locker. Blue is supposed to be such that it can be loosened with hand tools and red is supposed to only release with the addition of heat. I'd check the threads closely on the removed screws. BTW, I would definitely recommend Loctite blue for those screws. I've seen too many air conditioner shrouds along the highway, and had found some screws on my units beginning to back off before I started using the stuff.