I'm attempting to scan with Canon MX 892 on a 2009 iMac running mac os x 10.6.8. Any time I try to open MP Navigator EX 5.1, a message is displayed stating "The login account does not have the required privileges to access the specified folder."
I have the exact same problem and had the exact same problem, but I found the solution. The problem stems from using the incorrect software with the printer. By default, Mac will attempt to setup the printer with the less than ideal software.
What you should do is delete the printer from your system settings to start from scratch. Go to add a new printer. I'll assume you know how to do this and not bother explaining it step by step.
When you select to add a new printer you'll see a window like this one (screenshot attached). Select the MX892 printer from the list as I've done in the screenshot and notice at the bottom where it says Use: AirPrint.. This is the software you DO NOT want. You want to select the drop down and choose 'Canon MX892 Series'. Once you've selected this and clicked Add, your mac will proceed to download the REAL Canon software for this printer and install the printer for your use.
Once your system is done doing its thing.. that's it.. Now when you go to print something you'll notice that the settings will be slightly different (illustrated in the second screenshot) The particular setting you want for economy aka draft printing will be fast and grayscale as I've selected in the screenshot.