Strange Z axis movement in 2d sidescroller??

So I've been working on a 2D sidescrolling shooter for a while now and I've come across a snag. For some reason after implementing a "mouse aim" script to rotate the players firearm to the position of the mouse it tends to allow the player to move on the Z axis when the weapon is pointed in certain angles. I cannot for the life of me figure out how and why it is doing this. I also recently added a weapon swapping script that when switching to melee and deactivating the firearm with the "mouse aim" script it won't allow me to move forward. o.O

Any help would be greatly appreciated here are the three scripts that I mentioned in the above paragraph.

Movement Script

     var walkSpeed : float = 2.0;
     var runSpeed : float = 4.0;
     var fallSpeed : float = 2.0;
     var gravity : int = 20.0;
     var Jump : int = 0.0;
     var moveDirection : int = 1;
     
     private var velocity : Vector3 = Vector3.zero;
 
 
 function Update () 
 {
     var controller : CharacterController = GetComponent ( CharacterController );
 
     if ( controller.isGrounded )
     {
         velocity = Vector3 ( Input.GetAxis ( "Horizontal" ), 0, 0 );
         
         if ( velocity.x == 0 && moveDirection == 1 )                            //idle right
     {
     //animation goes here
     }
 if ( velocity.x == 0 && moveDirection == 0 )                            //idle left
     {
     //animation goes here
     }
 if ( velocity.x < 0 )                    //walk left
     {
     velocity *= walkSpeed;
     //animation goes here
     }
 if ( velocity.x > 0 )                    //walk right
     {
     velocity *= walkSpeed;
     //animation goes here
     }
 if ( velocity.x < 0 && Input.GetKey("left shift"))                    //run left
     {
     velocity *= runSpeed;
     //animation goes here
     }
 if ( velocity.x > 0 && Input.GetKey("left shift"))                    //runright
     {
     velocity *= runSpeed;
     //animation goes here
     }
         
     }
     if ( !controller.isGrounded )
     {
         velocity.x = Input.GetAxis ( "Horizontal" );
         velocity.x *= walkSpeed;
     }
     if ( velocity.x < 0 )                //last move direction left
     {
         moveDirection = 0;
     }
     if ( velocity.x > 0 )                //last move direction right
     {
         moveDirection = 1;
     }
     
     velocity.y -= gravity * Time.deltaTime;
     controller.Move ( velocity * Time.deltaTime );
     
 }
 
 

Mouse Look Script

     var mouse_pos : Vector3;
     var target : Transform; //Assign to the object you want to rotate
     var object_pos : Vector3;
     var angle : float;
      
     function Update ()
     {
     
     mouse_pos = Input.mousePosition;
     mouse_pos.z = 0; //The distance between the camera and object
     object_pos = Camera.main.WorldToScreenPoint(target.position);
     mouse_pos.x = mouse_pos.x - object_pos.x;
     mouse_pos.y = mouse_pos.y - object_pos.y;
     angle = Mathf.Atan2(mouse_pos.y, mouse_pos.x) * Mathf.Rad2Deg;
     transform.rotation = Quaternion.Euler(Vector3(0, 0, angle));
     
     }

Weapon Swap Script

 var Weapon01 : GameObject;
 var Weapon02 : GameObject;
 
 function Update () {
     if (Input.GetKeyDown (KeyCode.Q))
     {
         SwapWeapons();
     }
 
 }
 
 function SwapWeapons()
 {
     if (Weapon01.active == true)
     {
         Weapon01.SetActiveRecursively(false);
         Weapon02.SetActiveRecursively(true);
     }
     else
     {
         Weapon01.SetActiveRecursively(true);
         Weapon02.SetActiveRecursively(false);
     }
 }

As stated any help would be greatly appreciated, I'm stumped :P