Terrain Collision Glitch

I created a terrain and i added my player prefab.

That done this : My player collide with a slope, and the collision glitch. Why? Here's my movement code:

 #pragma strict
 @Header("Statistics")
 @Range(0,5)
 var speed : float;
 @Range(0,50)
 var jumpForce : float;
 var playerRigidbody : Rigidbody;
 var inputAxis : Vector3;
 
 var grounded : boolean;
 
 @Header("OverlapSphere")
 var groundSphereRadius : float;
 var groundLayers : LayerMask;
 var debugCollision : boolean;
 var check : Vector3;
 @Header("Debug")
 var realSpeed : float;
 var speedMultiplicator : float;
 var smoothTime : float;
 
 function FixedUpdate () {
     var horizontalDivisor : float;
     inputAxis = Vector3(Input.GetAxis("Horizontal"), 0, Input.GetAxis("Vertical"));
     var realInputAxis : Vector3;
     if(Input.GetButton("Run") && grounded){
         speedMultiplicator = 2;
         horizontalDivisor = 2;
     }else if(Input.GetButton("Crouch") && grounded){
         speedMultiplicator = 0.5;
         horizontalDivisor = 1;
     }else{
         speedMultiplicator = 1;
         horizontalDivisor = 1;
     }
     
     realInputAxis = Vector3(Input.GetAxis("Horizontal") / horizontalDivisor, 0, Input.GetAxis("Vertical"));
     
     realSpeed = speed * speedMultiplicator;
     var transformedRealInputAxis = transform.TransformDirection(realInputAxis);
     playerRigidbody.MovePosition(transform.position + transformedRealInputAxis * realSpeed * Time.deltaTime);
     
     if(Input.GetButtonDown("Jump") && grounded){
         playerRigidbody.AddForce(Vector3.up * jumpForce * 25, ForceMode.Impulse);
     }
     
     var hitColliders = Physics.OverlapSphere(check + transform.position, groundSphereRadius, groundLayers);
     if(hitColliders.Length == 0){
         grounded = false;
     }else{
         grounded = true;
     }
     
     //Fake friction
     var easeVelocityFactor : float;
     easeVelocityFactor *= 0.75;
     
     playerRigidbody.velocity.x = easeVelocityFactor;
     playerRigidbody.velocity.z = easeVelocityFactor;
 }
 
 function Update () {
     
 }
 
 function OnDrawGizmosSelected() {
     if(debugCollision){
         if(grounded){
             Gizmos.color = Color.green;
         }else{
             Gizmos.color = Color.red;
         }
         Gizmos.DrawSphere(check + transform.position, groundSphereRadius);
     }
 }