I have also experienced this problem at the office when use the Canon PIXMA MX870 printer. I fix this only update the latest version of MX870 MP Driver V1.06. Then there are no the notification about the printer unplug. I download the latest drivers ...
Oh my god, Canon USA is maintenance. How long it will fixed. But this site (www.canonprintersdrivers.net) helps me to find canon drivers while Canon USA maintenance. But that site can not do more, It only provides little informations about USA canon....
