Unread email keeps appearing in outlook

Hey guys,

I have just received this problem via our logging system:

Marian
She receives some emails and she views them but after about a week they come up as being unread again. This is happening intermitantly some weeks she will have 10 emails that do that, and other weeks she will have one email that does that. This has been happening for about 8 weeks.

Would you have any suggestions on how to fix this?
we are running exchange server 2000 and outlook2002 on the clients side.

Thanks
Matt