dont have that model, but I assume that error means your encoder is dirty.
re-clean, re-calibrate & re-test through the service menu. dont use full strength alcohol (and never use roland cleaning stuff!), cant remember the percentage, but its on this site soemwhere. if still dirty, remove the strip & flip it to the other half if you havent flipped it yet. It may also help to clean the electronic eye, but be careful not to damage it getting it out & back in straight.
also, clean the track that the carriage rides on & lube it a very little bit with 3in1 oil. our wheels/bearings(?) in the carriage got dirty & was causign an encoder error recently and this fixed it.