Hi Stagen. The following error is a diagnostic tool usually used for setting up the drives. when the drives are adjusted the following error should be a "dither" .0000 / .0001 back and forth.

I think you are look at the motor trying to "decide" which "tach pole" to look at. The motor will jump back and forth "this one, oh no wait, this one, no wait " etc.
You will need to clean the motor tach.

The tach is located under the encoder mount under the cap.
Loosen the "coiled" strain relief and the cable will be able to be slid forward giving you enough room to work.

You will need electrical contact cleaner and possibly a rubber eraser. Blow out any dust 1st. then spray down with cleaner. look carefully at the copper tach and clean up any crud in that area.
carefully reassemble.
Kinda of a pain, but sitting for a long time, crud will grow.

Sportybob