Since the area no longer exists, the script doesn't know to where users should be redirected. By deleting the area, you deleted the .htpasswd file that was holding the user information for that area. Although the user still appears as being a part of that area within the "View" screen of the admin control panel, his password is not recorded with the new .htpasswd file. In this case, you will need to reconfigure the area by clicking on the "Area Management" link, selecting the area in question, and clicking the reconfigure button.