On buying a Canon D660u scanner, I was unable to successfully load the software in spite of following the instructions in the manual. I was getting an error message 'unable to locate the TWAIN driver'. An hour on the phone with the Canon help desk didn't help either. As advised by the help desk chap I took my pc in to him at Canon and he spent another fruitless hour trying to load the software. He became convinced that it was a Windows problem, and advised me to format my h/d and do a fresh reload of Windows ME. This was done, and sure enough the scanner software loaded without a hitch and the scanner worked just fine. A couple of weeks later I was getting the 'unable to locate the TWAIN driver' message again. I am unable to use the System Restore function om ME as it had been cleaned out to get rid of a virus, and I hadn't realised that it didn't restart automatically.
No amount of uninstalling and re-installing of the scanner software makes any difference. After insalling the Canon scanner icon appears in the scanners/cameras folder in control panel, only to dissapear after a couple of days.
Any help to get the thing going without reformatting/reinstalling Windows would be appreciated.

System specs. Gateway P111 with 128 meg ram. Windows ME,
the scanner is connected by usb cable to one of the two usb ports, a printer on the other usb.