If all else fails - find an identical tape (same brand, same model, year of manufacture, etc.) that you don't need. Take out the screws and carefully separate the two sides of the tape you don't need. Be careful to make sure the runners and wheels, etc. stay in position.
Now do the same with the tape you're having problems with. Compare the insides and see if something is out of place. If there is something broken or out of place - fix it and see if it will work.
If that fails, take the tape (tape only) out of the problem tape, and put it in the other tape case.