Outlook 2003 Can't Open Some Messages

Heya everyone. I work for a credit union, using Outlook 2003 on all of our workstations. One of these workstations is having a problem opening some messages, and I was hoping someone could help. Being that it's the CEO's computer adds just a little bit of stress. rolleyes

Anyway, it looks like all the messages in his "inbox" folder open fine. However, he's kept quite a few messages from past years in a separate folder, and some of those won't open. When I double-click on them, I get the message "Can’t open this item. This operation is not supported until the entire message is downloaded. Download the message and try again." This is a POP3 account, so I'm assuming it's not an issue with an OST file. Also, the message is marked for downloading, but using the "Process Marked Headers" option does nothing. Send/Receive options are set to download everything for his account.

Any insight from anyone would be greatly appreciated. Thanks in advance.