Have you replaced any of the ink cartridges recently?
I don't have this printer but found the following from a quick google search on this thread title:
Service error 6502 is an ink tank position sensor error.
Service error 6502 generally means that your ink cartridge chips cannot be recognised. The primary cause of this is the blockage of the LED. Ensure that no tape, glue etc is covering the chip or LED on the rear of the cartridge.
Also - the following solution was posted on another forum
"Took cartridges out of printer, I could see some small smudges and I just gave them a quick wipe over the computer chips and that fixed it. "
Hope this helps!