In my instance, there was nothing wrong with the tape (not sticky) nor my machine. The locked problem was caused by the "button" that unlocks the tape when it is being played in the machine. For some reason, the button had fallen out of position so that when inserted into the player, the player could not unlock the tape. The solution is to unscrew the back, remove the back, carefully turn the whole mechanism over, carefully remove the lock button, put it back so that it is back in the correct position, turn the whole mechanism back over and re-screw the back onto the tape. Make sure the tape does not come out of the guides or that any part falls out. The button to which this refers is the one mentioned in other solutions where you put a screwdriver into the hole. That was the problem with my tape where that toggle button was out of position. This solution corrected my problem.
Vbasic, July 2016
