First you need to follow the instructions for installing the scanner.
It is important whether you connect the scanner before the software is
installed and whether you work from the new hardware found box or just
install the driver as software. It sometimes varies between operating systems
Sometimes the twain files can become corrupted. Since other devices like digital cameras
use the twain files they aren’t erased with a driver uninstall or
overwritten with an install. If the twain files are gone the driver
install will also install them.
Uninstall ScanGear (I think that is the Canon driver software
) and remove the scanner if it is still showing in device manager and control panel under scanners. Unplug the USB.
Do a search for twain
and delete all you find in the Windows folder. There is probably a
folder and several files – delete them all. Do not remove any twain
files not in the Windows folder.
Dig out the instructions and reinstall the scanner exactly according to them.