This film back is defective. I have tested it on a Rolleiflex SL66 and was able to expose a roll of 120 film with 12 exposures; however, I had to take out the film in a changing bag because the advance knob of the film back was locked after the last exposure. 

When mounting the film back now, the winding crank of the camera can not be advanced. I don't know, where the problem is. When I'm mounting a different film back, the camera works fine.