I cannot get my Cannon MP190 to scan via the PC

I cannot get my Cannon MP190 to scan via the PC, or save a manual scan to PC. I'm running Vista 64 bit OS. I've tried reinstalling the MP190 software, downloading the latest 64bit software from the Cannon website, and reinstalling only the scanner drivers without any success. Manual scanning (copying) works OK, but I've tried using the Navigator dialogue box, and saving a manual scan, only to have my PC go into a long sulk before telling me there is insufficient Memory (hard to believe on a machine with 4GB RAM!). Any suggestions for a cure would be welcome.