Fuond this,hope it helps.
When trying to copy Outlook storage file (*.pst files) when Outlook is running you'll see "The process cannot access the file because it is being used by another process" error message in your Backup Magic log file. That means Outlook has exclusively locked the file and it can't be read or copied by other programs until you close Outlook.
Solution is to exit Outlook before starting backup. If, after exiting Outlook, you still encounter the problem, some other programs, components or services may still use Outlook on the background. You need to close them to get full access to the files you want to copy.
The following Microsoft knowledge base articles may provide some help:
196366: Why Outlook May Continue to Run After Exit
221201: Outlook Will Not Shut Down with WinFax Pro Installed