Player One vertical film reel sensor break missed sensor. If this error appears, the machine should count 24 seconds for one full revolution of the frames. If the error persist, try one of the following: 

1) Make sure that the rubber sensor break attached to the "Number 7" frame is properly attached and in good condition. 

2) Check the alignment of the sensor break and the film reel sensor. Make sure that the sensor didn’t vibrate loose which causes the rubber break to miss the optic beam with each revolution. 

3) Replace the vertical film reel sensor