Unlimited engine option does not work I  work in a school and all my Lego NXT bricks have the same problem. Unlimited choice in the activation time engine does not work. The other functions (rotation, and second degree) are going well. So I can use my probes and so I am very limited in the tasks to be performed. 

I've done these actions, but without success:


Reset On my brick 
Update Bricks
Update The program to version 1.31
Contact My representative
You need to ensure that your program has a way to stay alive (wait block, wait for sensor, etc...), otherwise as soon as the program ends all motors are stopped.