This problem can occur when file that maintains the Navigation Pane settings becomes corrupted. This file is called profilename.xml, where profilename is the name of your Outlook profile. This file is stored in the following folder:
C:\Documents and Settings\username\Application Data\Microsoft\Outlook
Windows Vista, Windows 7
To resolve this problem, use the following steps.
On the Start menu click Run.
In the Run dialog box, type the following command:
Note: There is a space between “Outlook.exe” and “/resetnavpane”
Note If you are using Windows Vista or Windows 7, you may not see Run on the Start menu. In this situation, use the following steps to locate the Run option.
On the Start menu click All Programs.