Cannot Start Outlook: ".pst is in use"

Cannot Start Outlook: ".pst is in use"

This is a message that popped up this morning, when I opened oulook. Fixt it:

1. Your .pst file is corrupted.
2. Your .pst file is in use by another program.

1 - Your .pst file is corrupted.

There are plenty of good guides on how to repair your .pst file:

Guide for repair of outlook .pst file. 

This can also help if outlook fails to index.

2 - Your .pst file is in use by another program.

After a few years of use a .pst file can become very large. Mine is currently at 9.0GB. This means that a backup / sync programs such as syncbac, can take several minutes to backup / sync the .pst file.

During this time you will receive the error message ".pst file in use", if you open outlook. 

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