We recently came across error code 6A81 on our Canon Pixma MG5250 Printer (using PGI-525/CLI-526 range cartridges). The error could also occur on other printers in this range.
The error code is basically caused by an obstruction within the printer, usually a paper jam but could be any foreign body that has found its way into the printer (those with young children will understand!). The obstruction stops the carriage and print head from moving into the correct position when powering up the printer. The print head should come to rest at the right hand side of the carriage and position itself over the waste ink sponges. If the print head is unable to do so, it returns the '6A81' error message.
You can see from the picture, the position of the two waste ink sponges towards the right hand side. The sponges are spring loaded and move backwards and forwards when the printer initialisation occurs upon start up.
The problem in our case was caused by two pieces of torn paper. One at the far right of the printer which was simple to remove, but the other was stuck in a small opening behind the spring mechanism for the waste ink sponges. This was preventing the sponges from being moved freely and seated correctly, which in turn meant that the print head was unable to pass over them and come to rest in the correct position.
To remove the torn paper we turned off the power to the printer (to prevent any damage to the carriage mechanism) and used a pair of tweezers to carefully pull the offending article through the small gap. We missed this hidden piece of paper the first time we checked for obstructions so it's worth shining a torch in and having a good nose around!
Close your printer lid, power on the printer and et voila... Canon error code 6A81 is no more!