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Each time I have seen this come up, it has been a problem with the driver on the computer. What I would suggest doing is going to your control panel - programs and uninstall all canon software for the printer. Then go to the following page to download the latest version. After doing that, reboot and then reinstall the software, connecting the scanner only once it tells you to.
You will find downloads under both the "Drivers" and the "Software" sections.