When you start Outlook, you may receive the following error message:
File <drive and path>\xxxx.pst is in use by another application. Close Microsoft Exchange and all other mail-enabled applications and try again.
Cannot open your default e-mail folders. The file <drive and path> outlook.pst is in use and cannot be accessed. Close any application that is using the file, and then try again. You might need to restart your computer.
This problem occurs even if you have full access permissions and there is no password on the Outlook Data (.pst) file. The problem may appear intermittently. This can also affect an Offline Outlook Data (.ost) file.