I've run a couple of Shadows for a few years. Cannot say I have seen that error.
Are you generating the code with the assistance of CAM software? I ask, because the Shadow is fussy about arc center accuracy and it has to be calculated 'dead nuts on' or it will protest.
Also, I believe if you are working in absolute coordinates (G90 mode) then, the arc centers must be described in absolute coordinates. No mixing absolute XY with incremental IJ, which most other controllers can do.
AFAIK, Shadow can use IJ directly, or it will translate the arc code that way when importing it. No need to fuss with /X and /Y for arc centers.