I found an overview of POST (Power On Self Test) Error messages. It says:
21.07 means right Prinhead jetstack termistor out of range. Replace the printhead.
As for 08,009.65 This is an error due to an unexpected message received while homing the Cap/Wipe/Purge assy, usually during system initialization. And just like Michael52x says, due to a failure of the Y-Axis Encoder. This Encoder can be tested through diagnostic. You'll find the Y-Axis Encoder assy (a three legged black thing) on the left side of the drum. If you need to replace it the part number is: 650-4144-01 (Y-axis encoder kit, Phaser 850/860/8200)
But i'll go for Michael52x's suggestion, check for mechanical faults first. Could be a dirty pulse disc in the encoder assy...
Good luck