It certainly looks as it's something in the users 'profile' (sorry, that's a Windows term). But only Canon knows what that 'something' is. They designed it and they programmed it.
I'd look around for a file created that exact moment in some temporary storage area.
We have an iMac running OSX 10.6.8. We have an attached multi-function Canon MX-360 which up until last week was working fine. We had to cancel a scan and the scan program froze. We executed a Force Quit and tried to re-scan but the ScanGear window freezes ... says "Scanning. Do not open the document cover" but nothing happens. The Cancel button is unavailable and we must Force Quit MP Navigator EX (not responding) again. We did send a report to Apple as the Force Quit program requested.
We then removed the program (using MacKeeper) and re-installed but the same problem arose on the first attempt to scan. The printer function works fine.
We installed the Canon software on two other computers ... my son's MacBook Pro as well his wife's Windows 7 machine ... the scan function works fine on both of these machines and thus it seems the problem is with the iMac. We suspect there is a file somewhere on the iMac that is preventing the Canon from completing the scan.
Can you offer some assistance please to get the iMac to stop freezing on the MX-360 scan function?