Compatibility mode is NOT needed with any version of Outlook on any versions of Windows. to Compatibility Mode You may receive an error message and Outlook does not start when you try to start Outlook on a computer that is running Windows XP (MSKB) Close Outlook.
At the Start search field on Vista or Windows7 Start menu or in the Start menu, Run command (Windows key R), type or /resetnavpane Then press Enter (or OK button) to restart Outlook.
Wait about five minutes or more for the mail spooler process to shut down or close Outlook and reopen.
Go to the Outbox and delete the message then put Outlook back online using the File, Offline menu.
To use this method, close Outlook then type outbox or store:mapi outbox in the Start search field.
In the Start search or Run fields or in Windows Explorer's address bar, paste the following and press Enter:%appdata%\Microsoft\Outlook This will open Windows Explorer to the folder where many of Outlook configuration files are kept.
Find and delete the file named for your profile with the extension XML.
Note: Make sure there is a space between the words.
If you are having problems using the switch, you can find and delete the XML file that holds the navigation pane settings.