)Quit Outlook.
2)Click Start, point to Find, and then click Files or Folders.
3)Type Mapi32.dll in the Named box.
4)In Look In, click to select My Computer, and click Find Now.
5)Right-click to select Mapi32.dll in the search results list.
6)Click Rename, type Mapi32.old, and press ENTER to accept the name change. If there are multiple copies of Mapi32.dll in the list, rename each.
7)Close the Find Files window and start Outlook.
When you start Outlook, it checks for the existence of necessary files.
In the case of Mapi32.dll, if it is not present at startup, Mapistub.dll is used. If for any reason Mapistub.dll cannot be found, Setup automatically attempts to replace both files.
NOTE: When you start Outlook and receive a prompt that files are missing, click "Yes" to allow Windows Installer to replace them.