object goes through walls(no, dats nnot what r u thinkig about)

so, i have cylinder that moves up and down, it has rigidbody and capsule collider elements attached. so the problem is that if i'm touching green wall, ball goes through it. but i'm sure its not because of its speed, i took into account it, and made max speed(its 15). this cylinder sometimes is working fine, but sometimes not. here's whats happening:

and here is how it has to be:

my controller script:

 var speed = 0.0f;
 var speedUp = 0.2f;
 var MUS = 0.1f;
 var UpSpeed = 0.0f;
 var DownSpeed = 0.0f;
 var cameraLose : Camera;
 var mainCamera : Camera;
 var collide : boolean = false;
 var CollideUp : boolean = false;
 var CollideDown : boolean = false;
 var maxSpeed = 2;
 var me : GameObject;
 var score = 0;
 var scoreGui : TextMesh;
 function Start () {
 
 me.GetComponent.<Renderer>().enabled = true;
 
 cameraLose.enabled=false;
 mainCamera.enabled=true;
 
 }
 
 function Update () {
 //checking speed    
     if(UpSpeed==15){
     UpSpeed=15;
     }
 
     if(DownSpeed==15){
     DownSpeed=15;
     }
     
     if(speed<maxSpeed){
     speed+=speedUp;
     }
     else{
     speed=maxSpeed;
     }
     transform.position += Vector3.right * speed * Time.deltaTime;
 slow();
 
 }
     
 
 function FixedUpdate(){
 //controlling object
 if(Input.GetKey("w")){
     if(CollideUp==true){
     UpSpeed=0;
     }
 
 }
 if(Input.GetKey("w")){
     if(CollideUp==false){
     transform.position += Vector3.forward * UpSpeed * Time.deltaTime;
     UpSpeed+=MUS;
 }
 }
 
 if(Input.GetKey("s")){
     if(CollideDown==true){
     DownSpeed=0;
     }
 
 }
 if(Input.GetKey("s")){
     if(CollideDown==false){
     transform.position -= Vector3.forward * DownSpeed * Time.deltaTime;
     DownSpeed+=MUS;
     }
 
 }
 }
 
 //speedUp controlling
 
 function slow(){
 if(Input.GetKeyUp("s")){
 
 do{
     DownSpeed-=MUS;
     //transform.position -= Vector3.forward * DownSpeed * Time.deltaTime;
     yield WaitForSeconds(0.01f);
     slowDownS();
     }while(DownSpeed>0);
 }
 
 if(Input.GetKeyUp("w")){
 do{
     UpSpeed-=MUS;
     //transform.position += Vector3.forward * UpSpeed * Time.deltaTime;
     yield WaitForSeconds(0.01f);
     slowDownW();
     }while(UpSpeed>0);
 
 }
 }
 function slowDownS(){
 if(CollideDown==false){
 transform.position -= Vector3.forward * DownSpeed * Time.deltaTime;
 }
 }
 function slowDownW(){
 if(CollideUp==false){
 transform.position += Vector3.forward * UpSpeed * Time.deltaTime;
 }
 }
 //collisons checking
 
 
 function OnCollisionEnter(collision: Collision) {
 
 //taking up points
     if (collision.gameObject.tag == "points"){
          score+=10;    
         scoreGui.text=score.ToString();
     gameObject.Find("score int").SendMessage("addScore", score);
  }
  //if we collide with obstacle die
  if (collision.gameObject.tag == "Obstacle"){
  collide=true;
   mainCamera.enabled=false;
  cameraLose.enabled=true;
  //me.GetComponent.<AudioSource>().Play();
  me.GetComponent.<Renderer>().enabled = false;
  die();
  }
      //make character not to go through walls
      if(collision.gameObject.tag=="wallUp"){
     CollideUp=true;
     }
     if(collision.gameObject.tag!="wallUp"){
     CollideUp=false;
     }
     if(collision.gameObject.tag=="wallDown"){
     CollideDown=true;
     }
     if(collision.gameObject.tag!="wallDown"){
     CollideDown=false;
     }
 
 }
  
 
 
 //killing player
  function die(){
  yield WaitForSeconds(0.2f);
 gameObject.Find("score int").SendMessage("show");
   Destroy(gameObject);
  }
 

and, yup i also tried to change fixed timestep in time manager, and i changed it to 0.02, i leaved maximum allowed timestep and time scale not changed.