Outlook cannot open .pst file which was in use by an unknown program

Question

We have a small "workgroup" network - 3 users, 3 computers running XP and MS Office 2003, 1 Buffalo TeraStation NAS, no servers.

On each PC, there is a U: drive mapped to the user's personal folder on NAS.

One of the users intermittently got an error when opening his Outlook
"Unable to open your default e-mail folders. The file U:\Mail\Outlook.pst is in use and could not be accessed. Close any application that is using this file, and then try again"

The problem happened on Sep 20 for the first time. I restarted NAS, restarted the computer, no joy. I killed the tasks of MS Security Essentials and Google Desktop, etc, that seemed to fix the problem. So I told the user to leave Outlook open, do not close it.
I checked this computer yesterday, Outlook worked fine. I ran scanpst.exe against the .pst file on NAS, I opened and closed Outlook a few times, the problem did not show up at all.

Today, the user called me because the problem came back again.
I spent an hour, but could not fix it regardless what I did. I even disabled all third party services and programs from MSCONFIG, but still no joy.

I installed "Unlocker", but it said that nothing was opening the .pst file, while there must be something! The other 2 computers are totally fine.

I am wondering if you know any program like "Unlocker" that is able to detect which program is using the .pst file. Or if you have seen this problem and know the solution?

Answer 1

The Unlocker application is good enough to give you an overview about the applications that might use the PST file. The problem might not be related to the Outlook at all. I would recommend deleting the U: drive. After this, remove (using Device Manager) the driver for the network adapter and reboot the machine. Re-install it, eventually change the IP address of the adapter and set it on manual, and then map the driver as another letter. Additionally, check the Firewall and disable it completely for the time being.

Try opening the PST file now. If I am right, the problem should be fixed.

P.S: Repair the Outlook installation and apply any available updates through Windows Update.