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

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