Sounds like something is blocked by a GPO. Are others experiencing the same issue? Is this an Exchange account? If so, what version of Exchange, what service pack level? What action are you attempting to perform? Has it ever worked? Please provide the details. Thanks!
If this is a POP3 account, then try scanpst. If that does not solve it you may need to create a new mail profile and move all the email into the new profile. Try uninstalling/re-installing Outlook first.