I just got this on my 360, I'm assuming it's gonna be very similar if not exactly the same on the 560.
It's really easy to get to, take off the right cover and then unclip the metal cover on the carriage that covers the PCB. The line sensor is on the right side attached with a ribbon cable and 2 screws. I just cleaned mine and the error went away.
The line sensor is part of service maintenance kit #3, so check the life of that, if it's getting up there then that might explain your error.