This is so weird that I just had to share...
A few nights ago I went to play my game and nada. A slight whirring from the disc drive, but aside from that nothing at all. No splash screen, nothing. It was doubly strange because I'd been playing about 5 hours earlier and had downloaded nothing and altered nothing at all in my game files in the interim. So I tried all the usual things to get it to play, still nothing. I concluded that my drive was broken. Then I tried to play Fallout 3. Discovered drive was not broken. 
By now I had accepted that something in my game was totally borked and decided to test without CC, as you do. Started dragging my Downloads folder to the desktop. All was going swimmingly when I got a Windows message: "Do you want to copy the READ ONLY file _EnableColorOptionsGMND.package from..."
I nearly choked on my coffee. I have no idea and still don't how that file became read only. No one uses this computer but me. I went and redownloaded CEP, deleted the offending read only file and all was fine again in my game.
I know this is probably a really boring post for the majority of people here, and I apologise, but maybe someone might find it interesting... ....I find it most interesting for the fact that the file appears to have spontaneously corrupted! And I'm also thrilled that thanks to that little Windows message I didn't have to go through the painful 50% method... which would have taken me days.