You are not alone with this problem. It would appear that BT have been fiddling with the BTMail system and they have somehow broken it and it is now throwing you out.
Try clearing your browser's history and cookies. If the browser has the option make sure you clear it "from all time".
Another thing that may help is to switch to 'None' view by going to the "Change View" button on the right hand side. This will apparently resolve the issue until a fix is available.
