What versions of Outlook and Exchange? Are you working in cached mode? Are
there any other error messages/numbers? Are there any errors in the
Application Event Viewer relating to Outlook or Office? What does your
Exchange Admin say about the issue? Are you the only one with this error?  

Usually that error indicates that the connection to the server was
interrupted, the usual suspects would be antivirus software scanning incoming
and outgoing mail or a firewall. If you're on a network, firewall on the PC
may not be required since there would be a firewall between the network and
the internet.