First Person Controller Collision Issues

I have the first person controller and a cube on the terrain in my scene. The box collider is checked on the cube.

I attached the following javascript script to my controller:

function OnCollisionEnter(col: Collision){

For some reason nothing is printed when the controller collides with the cube but the collision works and the controller stops moving.

Yep. The way to capture that collision is in a script attached to the object with the CharacterController. Then you have to use the OnControllerColliderHit() callback to capture the event.