If you Google this problem, Microsoft’s site shows up, so you assume that the solution might be a good one. Actually, it didn’t work for me and is not even related to the actual problem at hand since they refer to this being an issue running Outlook in compatibility mode.
The solution? simply run: outlook.exe /resetnavpane on a command line
in my case i had to specify the full path to the binary.
c:\Program Files\Microsoft Office\Office12\outlook.exe /resetnavpane