I have never had this problem before upgrading to Windows 10.
In the past when I put in a FULL large black cartidge and had a nearly full small black cartidge I had no issue with printing to grayscale.
I have an emergency situation and now cannot print an important overnite shipping label.
I had always been able to print black ink only without color ink.
Is this some change in Canon software? Related to Windows 10? Some other glitch that can be fixed?