Attaching items to e mails - very odd error message

I have a user trying to attach items from SharePoint libraries to e mails in
Outlook (2007). When she selects an item and tries to attach it she gets this
message "The operation is not supported until the entire message is
downloaded. Download the message and try again" which makes no sense in the
context. She is using an XP machine but I cannot duplicate this error on
either XP or Vista machines on the same network. No one else is having the
same problem. Anybody know a possible cause (and a solution)?