Removing and re-placing the assembly seemed to solve the problem. Thanks!
However, one suggestion about the instructions:
In Step 5, "Insert the assembly into the printer and push the assembly against the rear bracket," it would be helpful to note that the end of the assembly which is inserted into the rear bracket must fit into a rectangluar opening in order to be fully seated. So the assembly rod may need to be rotated just a bit.
If the lighting is inadequate, or one does not look closely, the rectangular end of the assembly rod might go unnoticed.
Just a thought.