The grub screw found in C23 is 5mm long, that means that the motor can't turn when the brass nut has been attached even though I have made sure that the screw is up against the flat side of the motor axle.
Am I doing something wrong or is the screw too long?
I ended up cutting the screw with a Dremel, that worked fine.
Then I forgot all about my post here, sorry. Thanks for the replies.
Later I found that bag C9 contained many short grub screws, I was only looking in bag C23 as that was the one with all the other parts for the step I was working on.