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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.

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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.

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I had this exact problem and closing Lync fixed it. – Puddingfox Aug 23 '11 at 14:14
Ran into the same problem, Microsoft Communicator turned out to be the greedy file handler. – Dan Ling Jun 21 '12 at 14:20
Lync is such a sticky piece of crap. Somehow Sametime must have been contagious. – MonoThreaded May 4 '15 at 6:22
Also applies to Cisco Jabber – Enilorac Jan 18 at 16:47
up vote 45 down vote accepted
  • 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
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Both this and the other answer proved to be very helpful for solving my problem. – Ro Yo Mi Sep 9 '14 at 18:54

I couldn't find any processes that had a lock on my OST. Further, closing Lync provided temporary relief since I actually need both programs running. I finally just threw in the towel and uninstalled both office 2010 and Lync 2013. I then re-installed office 365 (with Lync). After 2 days, I have yet to see this error again.

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protected by Community Jun 28 '12 at 19:40

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