Or the purge unit needs replacement.
Incidentally, the 6A00 error pertains to all Canon printers made in the last several years, its not just used in one model.

And it’s always a paper path error or purge unit.

The purge unit, called a spittoon assembly in an HP, Lexmark, and other inkjet printers, is where the print head assembly parks when not in use, also its other job is to clean and make sure the print head is clean and open for printing.

That is where you'll find the print head assembly parked on top of it.
It also has an electrical pump to milk the print heads and test for ink flow.

So clean all under where the heads are parked and on IP6600D models you can take out the heads just by clipping them out, and then clean well.

Also clean the purge unit out make sure all is clean.


Please come back and just gave a vote, it will gave me some satisfaction to know am helping some one so I will keep on helping.
All The Best: Pineworks