How can I run my Canon n1240u scanner on Mountain Lion?

I have an old Canon n1240 scanner and I've just tried to use it after recently upgrading to Mountain Lion on my MacBook Pro. I downloaded the latest CanoScan software but when I pressed 'Scan' I get the message, "Failed to open a driver". I've found some software that works but it is not free. It called VueScan. It looks OK, at least it works. The demo version places text on the scan so it's not really useable, but at least it gives one a good demo.

Help please. :-)