Outlook 2007 - A data file did not close properly

This error can be one of the more frustrating, both in Outlook 2003 and 2007. I have found that usually it is due to a rogue add-in that refuses to let Outlook close out properly. To test if this is the case you must run Outlook in safe mode by:

1. Click Start -> Run.
2. Type in outlook /safe and click OK.

If Outlook starts without the error then you can be assured that it is a result of an add-in. In most instances it is the result of either the Windows Search add-in or the Google Desktop add-in. Both can be disabled as a workaround by:

Outlook 2003:

1. Click on Tools -> Options.
2. Click the Advanced tab.
3. Click the COM Add-ins button.
4. Clear the checkboxes for the offending Add-ins.

Outlook 2007:

1. Click on Tools -> Trust Center.
2. Click on Add-ins in the left hand pane.
3. Click the Manage button next to the drop down that says COM Add-ins.
4. Clear the checkboxes for the offending Add-ins.

I have found that this usually fixes the problem, however sometimes it is necessary to uninstall the offending program completely.