You can find the extended error codes in the instruction help by right-clicking the MCT instruction. Looking at the list the error you're getting reads "Set the transform dimension of the source system to the number of axes in the system, up to three."
I would guess that you will similarly get an EXERR 4 once you fix that as you will need to do the same for your second MCT for the real axes.
I would guess that you will similarly get an EXERR 4 once you fix that as you will need to do the same for your second MCT for the real axes.