Outlook issue

I am having a problem at one of my clients that is really strange. I am running Exchange 2003 and a couple of the workstations have Outlook 2000. Inside Outlook 2000 some of the messages say “This item contains active content that can’t be displayed in the preview pane. Open item to read it’s contents”. But when I open the item it says “Can’t open this item”. This only seems to happen to e-mails that are from listservs and places like that. The problem doesn’t happen on Outlook 2003.

I have ripped out Outlook and can’t get this to go away. I think it might be related to Exchange 2003.
Any ideas??