There are a number of factors to consider. Is this an exchange server account? If so are you using Outlook in cached mode? If not an exchange server account is this a POP3 account downloading to a .pst file? You can try re-creating your profile through the mail icon on the control panel. Please provide the details and we will better be able to guide you. Thanks.
Try uninstalling Office and re-install it. Fixes most bugs or problems.