I logged in as that member and saw the board just as it is now with no message other then the pop up one that states you have to register now. I was afraid maybe I would see it in Maintenance Mode, but it didn't happen to me. I am thinking it might be something else.
Have them to go the internet explorer Tools Menu and in there Internet Options. What we're looking for is the Internet files "Settings" button after the Delete Cookies and Delete Files button. Have them click on that and see if they have it set to 'Every Time you Visit the Page', 'Never', 'Every Time You Start Up IE' or 'Automatically'.
I would recommend they set it to automatically and try accessing the board again. It definitely sounds like a browser cahcing issue, so hopefully this will take care of it for them. Don't worry about posting about things that are going awry FootsieBear, that's what we're here for.