Outlook fails to open with error: 'Microsoft Outlook' exited without properly closing your Outlook data file

After shutting down Outlook forcefully and trying to restart it, the following error is displayed:

'Microsoft Outlook' exited without properly closing your Outlook data file. 'Microsoft Outlook' must be restarted. If this error message recurs, contact support for assistance.

Outlook then exits.

I've found that for me this occurs because Outlook crashed for some reason but the Lync 2010 client still has a handle to the .ost file. Exiting Lync completely allows Outlook to restart.

• Run Process Explorer and choose "Find Handle or DLL" from the Find menu.
• Search for '.ost'. This will display all open handles to your Outlook data file.
• Choose to close all handles to your .ost file
• Start Outlook again
• optionally - run C:\Program Files (x86)\Microsoft Office\Office14\SCANPST.EXE