Character Controller falls over when mid-air or when climbing steps.

Hello, I'm currently working on a Diablo-style RPG and I already ran into some problems. My player movement script works fine, as long as I'm not in mid-air or try to climb steps, then my character falls over and starts glitching.

Here's a video:

Here's my script:

Code (JavaScript):

1.  
2. #pragma strict
3.  
4. @script RequireComponent(CharacterController)
5.  
6. var gravity : float;
7. var maxSpeed : float;
8. var speedAnim : float;
9. var bulletSpeed : float;
10. var fireDistance : float;
11.  
12. private var moveDirection : Vector3;
13. private var moveGravity : Vector3;
14. private var moveSpeed : float;
15. private var playerPosition : Transform ;              
16. private var destinationPosition : Vector3;
17. private var destinationDistance : float;          
18. private var animator : Animator;
19.  
20. function Start() {
21.     animator = GetComponent("Animator");
22.     playerPosition = transform;                          
23.     destinationPosition = playerPosition.position;
24. }
25.  
26. function Update() {
27.     destinationDistance = Vector3.Distance(destinationPosition, playerPosition.position);
28.     var controller : CharacterController = GetComponent.<CharacterController>();
29.     animator.SetFloat("Speed", speedAnim);
30.     moveDirection = transform.TransformDirection(Vector3.forward) * moveSpeed;
31.     moveGravity = transform.TransformDirection(Vector3.up);
32.     controller.SimpleMove(moveGravity * gravity);                    
33.        
34.     controller.Move(moveDirection * Time.deltaTime);
35.     if (Input.GetMouseButtonDown(1)&& GUIUtility.hotControl ==0)
36.     {
37.          var playerPlane : Plane = new Plane(Vector3.up, playerPosition.position);
38.         var ray : Ray = Camera.main.ScreenPointToRay(Input.mousePosition);
39.         var hitdist : float = 0.0f;
40.         if (playerPlane.Raycast(ray, hitdist))
41.         {
42.             var targetPoint : Vector3 = ray.GetPoint(hitdist);
43.             destinationPosition = ray.GetPoint(hitdist);
44.             var targetRotation : Quaternion = Quaternion.LookRotation(targetPoint - transform.position);
45.             playerPosition.rotation = targetRotation;
46.         }
47.     }
48.     moveDirection.y -= gravity * Time.deltaTime;
49.     controller.Move(moveDirection * Time.deltaTime);
50.  
51.     if(destinationDistance <0.5f)
52.     {
53.         speedAnim = 0.5f;
54.         moveSpeed = 0f;
55.     }
56.    
57.     if(destinationDistance > 0.5f)
58.     {
59.         speedAnim = 1f;  
60.         moveSpeed = maxSpeed;
61.     }
62.    
63.     if(destinationDistance > .5f)
64.     {
65.         transform.LookAt(destinationPosition);
66.     }
67. }
68.  

Thanks in advance for any help!

 

I think i know, what the problem is, but i still don't know, how to solve it. Apparently, the player only detects the mouseclick on the plane, because when i click directly on the cube the player tries to get to the point under the cube on the plane, which creates the glitch.

 

Is there really nobody, who is able to help me?