Installer pops-up every time

When starting Outlook, every time I need to go through some installation process before it actually opens. Sometimes this also happens when I open a message or do something else.
Why is Outlook doing this and how can I make it go away?

The first thing that you should do is to let it finish; it’s obviously trying to repair something and pressing Cancel won’t help with that.

If it can’t fix Outlook on its own, it will need some help. Running an “Office Diagnostics” or a “Detect and Repair” are the tools of choice for this. You can find these options in various locations;

• Via the Help menu item in Outlook
• By starting it from Control Panel-> Add/Remove Programs (Windows XP and previous) or Uninstall a Program (Windows Vista)
  Make sure you press the button Change or Repair and not actually the Uninstall button.
• Insert the installation CD/DVD of Outlook or Office, start setup.exe and choose the Repair function from there.

If you are not starting the repair process from a the installation CD/DVD already, make sure to keep it handy anyway as you could be asked to insert it during this process. After the process completes, check Microsoft Update for any additional updates that you may need to reapply.

If that didn’t fix the problem either or only for a short while, it is likely that you have (components of) multiple versions of Office installed on your system. While this works and is supported in various configurations, it could still interfere with normal operations of Outlook which makes it required to go to the repair process every time. An example is that when you are using Outlook 2003 and are using Word 2003 as your email editor but also have Word 2007 installed, Word could need to go through a repair process when you switch versions.

Another example of ending up with components of multiple versions of Office installed is when you did an upgrade and let the installer remove the old versions. While this does remove the old versions, it often leaves additional components installed (like Microsoft Photo Editor of Office 2000 for example). You should then complete the uninstall process via “Add Remove Programs” or “Uninstall a Program” section in Control Panel. Look for the version that you do no longer use and press Uninstall.

If you cannot find any old version there or the installer won’t let you remove the old version, then you can use the Windows Installer CleanUp Utility instead. If you cannot uninstall Office 2007 you should follow these directions instead.

If you completely uninstalled all the components of any version of Office and then reinstalled the version that you want to keep and you still get this issue, it is very likely that another program is breaking Outlook every time you are using it. The main suspects will be addins but also other mailing applications that you may have installed or applications that rely on Outlook such as faxing software.