I was trying to scan using Adobe Pro, and it wouldn't recognize the printer. I tried using MP Navigator and it was telling me that the scanner driver was not installed.
When you said every time you tell it to scan, did you press the scan button on the printer itself or from the program? I didn't try pressing the scan button on the physical printer itself, just from the applications. I'm not at home anymore, but I'll try that tomorrow.
Which drivers/apps from canon did you install? The ones from the CD or from their website? Sorry for all the questions, I'm just trying to duplicate your install as close as possible.