"Cannot start Microsoft Office Outlook" error

I had a user report that she could no longer get Outlook 2007 to open and was getting the error "Cannot start Microsoft Office Outlook. Cannot open the Outlook window." dialog box, as seen below.

I wasn't sure what was causing it, so I started my troubleshooting. I first tried opening Outlook in Safe mode, but that didn't help. I knew she has installed some Windows updates early today so I tried a system restore, but that didn't work. Then I turned to thinking her mail files were possibly corrupt, so I used scanpst to check them for errors and repair what it found. That didn't work either. I was stumped, so I turned to Google. It was then that I ran across what ended up solving my problem.

It was an Outlook switch I had never heard of before. resetnavpane, and it worked like a charm (thanks d-pabs). Here's how to fix it, and I'm going to assume you're using Outlook 2007. If you run into this issue while running Office 2003, the only difference is the path to the Outlook.exe file should be Office11, not Office12 as shown below

1. Go to Start->Run

2. Type cmd and press OK (alternatively, open a command prompt window however you'd like)

3. In the command prompt window, type "C:\Program Files\Microsoft Office\Office12\Outlook.exe" /resetnavpane and press Enter. Make sure you actually type the quotation marks with the path in this instance since it is required in order for the command prompt to recognize the path to the Outlook executable since there is a space in it.

4. This should start up Outlook and you should be able to get into your email again