TIH 2012 checking credentials on a non-existant network drive

I've recently added/changed the drive configuration on my machine and now can't change the drive designation for my external backup drive. Every time I try to change it, it keeps going round and round over credentials. I've been doing a search on this problem and while I see that the never ending credentials checking issue has plagued people since 2010 and may even exist in 2013. In my case, it's hanging up trying to get me to "edit credentials" for a network drive that is no longer attached - and never required credentials in the first place. Juggling drive letters is not an option as I'm unable to change the virtual CD that has taken over the drive letter that my backup drive used to have.

I'm running build 7119 and have downloaded 7133, but nothing addresses this issue in the release notes. Is there truly a fix someplace and I've just missed it? Any help would be appreciated!