Cannot Move the Items - Outlook 2007

I have an user in my Department that received the follow error message
"Cannot move the items. Your server administrator has limited the number of
items you can open simultaneously. Try closing messages you have opened or
removing attachments and images from unsent messages you are composing".
This message only appeared after moving from MS Outlook 2003 to 2007. I
have serveral users with 2007. Only one with the problem. I am the server
administrator, and have not changed any setting or limited any number of
items. Windows XP2 is the OS. Only about 10 items were been moved.

Thanks....