Power user cannot send emails, it stays in outbox

[rlim]

We have an Outlook 2003 client connected to Exchange 2000, and on that particular computer with Outlook 03, users cannot send emails out. It just stays in outbox, however once I set them as local administrator, the emails goes through. When the user was a power user, when Send and Receive button was pressed, nothing happen! All other workstations running on both Outlook XP and Outlook 2003 dont have this problem. Any suggestions would be appreciated.