I have the same problem;
GRT used to work, but suddenly stopped and now I can't restore single mailboxes anymore (see screenshot). As far as I know, nothing was changed recently.
We back up to tape (via temporary c:\temp folder) and there is enough space on the disk.
I don't see what's wrong or what might have been changed. What specific settings do I need to check?
thanks
***edit***
ok, I just saw that the logon account was hidden from exchange address lists. I will check tomorrow if things worked out.