I have this exact same problem - my N800 is a brick, because every time I reboot (even a battery-out reboot), I get this White Box and I cannot do anything else. Did you find a solution? Or was the solution what you suggested (keep rebooting until you can uncheck the applet)? I have tried this but have never been quick enough. Any help appreciated, before I have to do a hard reset and go through the pain of reloading all my applications.