The process cannot access the file because another process has locked a portion of the file

   If you just closed Outlook, it could take a while before it actually fully closes. Outlook could be running internal processes on the pst/ost file (such as Auto-Compact) or waits for another utility to finish its process such as an indexer utility (Windows Desktop Search, Google Desktop Search, etc…).
   Outlook might be closed but something is hijacking the outlook.exe process which has the lock on the file. As long as that process runs, you cannot do anything with the pst/ost files. Usually this is the result of a certain add-in that you have installed or an application that relies on the outlook.exe process such as Skype, fax software or having a mobile device connected to your PC. Outlook is then still running even when all Outlook windows are closed.

Wrong OS or OS version for application

   The error happens if you have run the wrong version of software on your system. For instance, if you have 32-bit Outlook on a 64-bit Windows, you might had run the 64-bit software version in trying to match the bit-ness of your Windows OS. However, the Widnows OS bit has no play here. We have provided 32-bit and 64-bit version of software because your Microsoft Outlook can be either 32-bit or 64-bit. You should match the bit-ness of the Outlook and not the Windows OS.

Is there a way to view pst/ost files without having Outlook installed?

   PST Walker does not require MAPI or Microsoft Outlook to be installed on the target computer. This pst/ost viewer does not use libraries and tools for viewing pst/ost files provided by Microsoft. Instead, PST Walker reads, scans and recognizes the contents of the initial Outlook data file.

My outlook data file has gone over the 2GB limit, the outlook tools (2GB fix and scanpst) don't correct the problem. Is there any way to recover?

   PST Walker can open corrupted PST, OST files and bulk export them to MSG files.

Is there a way to recover accidentally deleted email?

   PST Walker can find items that were permanently deleted instead of moving to the Deleted Items folder in Outlook ("hard deleted" items) and items that are no longer associated with any folder in Outlook ("orphaned" items).

I need to restore a mailbox from a pst file. I can see the hard deleted messages, but can't figure out how to use the bulk save as. I can save one message at a time, but need to use the bulk option.

   Select a range of email (i.e. from your "Hard deleted" folder) that you want to bulk save and select "Export(Bulk Save As..)" from the "File" menu. To select a range of email just single-click on the first email, then holding down the SHIFT key, click on the last email in the range you want to select, all the emails in that range will be highlighted. You can also single-click an email, hold down the SHIFT key and use the down arrow to scroll down the list, highlighting each email as you go.

I notice though that the contacts, appointments, notes, tasks can only be saved as .msg files. Does this mean I can't extract contacts, appointments, notes, tasks?

   No, this does not. The contacts, appointments, notes, tasks can be saved as .msg files. Outlook does open this .msg files as contacts, appointments, notes, tasks items.
How can I easily export them back out and into outlook?
The easily way to export them back out and into outlook is:
1. Bulk export contacts, appointments, notes, tasks into .msg files
2. Bulk import them into outlook using MSG 2 PST (demo version available)