I just had this exact issue. Clearing the \Roaming\Remote Utilities folder fixed the issue. I kept my address books separate so nothing was affected there. I have also found the the address book XML files can get corrupted easily, so I make frequent file backup of those.
I use local address books, and on occasion, I have found that the XML file gets corrupted. When I do a big change, i make a backup of those files just in case.
This problem just cropped up for me. My guess is you guys glued down this issue and Microsoft through .NET update unglued it for you. I'll keep this thread subscribed to see if you guys are able to glue it down again.