It’s a Tac50-04. That’s the same as a 681 in IMS. Typically those are intermittent faults, usually related to grounding. It should clear with a power cycle but if not, make sure you have P24V to the encoder. Comes from F3 on the IOC. If that’s good, you need to look at the encoder interface card in the motor junction box, it turns 24v to 5v and has a plug connector. After that, take your pick of boards to swap, then the encoder.
