physics.gravity with tilt game

Am making a tilt game by applying gravity on a marble which makes it move on the plan in this case the maze.

The ball have a rigidbody with mass set to 1 .The plane model have 2 parts the plane and the walls .

the plane have a metal material and smooth sphere colider unchecked .The walls have a custom material with dynamic and static friction set to 0 and both friction and bounce combine set to minimum .

the problem now is that if the marble is at a corner where it colid with 2 edges of the wall or if i manage to keep the device leveled long enough for the marble to be still it will get stuck .

Turning off and on the smooth sphere colider on the wall will unstuck the marble any idea what might be causing this ?

the code am using for moving the marble is

// Move object in XZ using accelerometer (home button at right hand)
var speed: float = 2.0f;
function Start(){
}


function Update(){
var xmovment: float = -Input.acceleration.y;
var zmovment :float = -Input.acceleration.x;

Physics.gravity= Vector3(zmovment*5,-15,xmovment*5);

}

I suspect that the rigidbody went to bed: when a rigidbody stands still for a while, it goes to the sleep mode. Try this solution:

function Update(){
  if (rigidbody.IsSleeping()){
     print("Wake up little Suzy!");
     rigidbody.WakeUp();
  }
  ...