I have the same issue--and have since the Canon software was replaced with Image Capture. For me, though, it only happens when I use higher settings:
-Thousands of Grays and 150 dpi _never_ works
-Thousands of Grays and 75 dpi, no problem
-256 Grays and 1200 dpi, no problem
-256 Grays and 9,200 dpi, no problem
This reeks of a driver bug (numerical overflow?).