Exchange 5.5 Outlook Web Access

I have Exchange 5.5 running on a 2000 server. I have a few users who access E-mail from home through Outlook Web Access who are having problems deleting files. They click the checkbox next to the message and click delete, but they still show in the inbox even after hitting F5 (refresh). They do show in the deleted items folder, but won’t seem to get out of the inbox. Any ideas?