Error Message:

The operation failed due to an installation problem. Restart Outlook and try again.

I received this error message this morning when I opened Outlook 2003 with a new user profile. It opened fine with the local Administrator account.

I checked the Windows Event Viewer and there’s a “Warning” entry there for MsiInstaller (Event ID 1004) with a description of “Detection of product… The resource ‘HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Common\UserData’ does not exist.”

Doing the following fixed the problem for me:

1. Start -> Run -> type in regedit.
2. Go to HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Common (or HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook as others have pointed out, please check your event logs to see which one you need to select (thanks to Supercow for noticing this)).
3. (I recommend that you back up your registry first before making any changes) Right-click on Common -> New -> DWORD Value. Name it UserData.
4. Double click on the DWORD value that you just created (i.e. UserData) and set Value data: to 1.
5. Close the Registry Editor and open Outlook again.