ERROR: Outlook 2010 won't start / unable to access Mail Control Panel item

Try this:

Start Run outlook.exe /resetnavpane

OR

Go to Start > Regedit

1. Locate HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Windows Messaging Subsystem
2. Delete the Profiles key under the Windows Messaging (Subsystem) key.
3. When you start Outlook it will prompt to Repair.