What operating system are you using?
If you are using a Mac, the original setup CD will not work with the newer OS versions.
Try trashing the current driver and download again the latest version from the Canon website.
The old driver should be sent to trash before downloading the new one, to ensure the old one does not get accidentally used.
What version of OS X are you using?
Ok, can you try scanning from a different user account or guest account on the Mac and let me know if it works ok there?