I know that the rotation indicates that something is not perpendicular to something else, but I am having trouble visualizing what. Before I give myself a headache, I thought I'd ask if anyone else has tracked down and fixed a similar problem.
For reference, it is an iOptron CEM-60. I recently re-balanced everything, and am happy with tracking, guiding, etc. The scope is a 200mm Newtonian, mounted with the focuser and camera down, in the zero position.