The only thing I can think of to suggest is (if you are willing!) try running Friting as administrator. This sounds to me like a permission problem somewhere (combined with a Fritzing bug where it doesn't deal well with file errors). As administrator it should be able to write pretty much anywhere (which may or may not be desirable 
). If that works then we need to figure out what new file has been written and look at the permissions on where it is. The only other thing I can think of is to use the Microsoft trace program (which I have heard of but never used) to see if it can tell you what file it is trying to open when it fails (as I've never used it, I don't know if it can do this).
Peter