I found this problem coming up after I:
* Had a mesh that I wanted to adjust
* Detached skin & adjusted the mesh by moving faces
* MOVED/ROTATED A CONTROLLER which had Orient Constraints & Point Constraints on a bone for the mesh
* Tried to re-bind the bones & skin, which caused the error
The solution was: Delete the moved controller, then delete any IK handles upstream of the moved controller (maybe even all of them).