Cannot receive, Outlook 2003

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Here is my error message:

Task Receiving Error (0x8004210E): 'Your mailbox is temporarily unavailable
because another email massage is being delivered to it or another mail
application is accessing it. The server responced: ERR box locked'

I think I shut down all Firelwall, Norton etc. I have the settings right as
well. I can send.

Any ideas?
.