TGB Physics issues

function playerNinja::onLevelLoaded(%this, %scenegraph)
{
   // Define the player global variable
   $pNinja = %this;
      
   // Player movement functions
   moveMap.bindCmd(keyboard, "left", "playerLeft();", "playerLeftStop();");
   moveMap.bindCmd(keyboard, "right", "playerRight();", "playerRightStop();");
   moveMap.bindCmd(keyboard, "space", "playerJump();", "");
   
   // Tell the physics system to check collisions carefully!
   $pNinja.setCollisionMaxIterations(2);
}

function playerLeft()
{
    $pNinja.moveLeft = true;
}

function playerLeftStop()
{
    $pNinja.moveLeft = false;
}

function playerRight()
{
     $pNinja.moveRight = true;
}

function playerRightStop()
{
     $pNinja.moveRight = false;
}

function playerJump()
{
    $pNinja.setLinearVelocityY(-225);
}

function playerNinja::updateMovement(%this)
{
    if(%this.moveRight)
    {
        %this.setLinearVelocityX(40);
    }
    
    if(%this.moveLeft)
    {
        %this.setLinearVelocityX(-40);
    }   
    
    if(!%this.moveLeft && !%this.moveRight)
    {
        %this.setLinearVelocityX(0);
    }
    
    // Save the current y velocity so it can be reset.
    %yVel = $pNinja.getLinearVelocityY();
               
    // Cast a collision downward to see if there is a platform close by.
    $pNinja.setLinearVelocityY(100);
  
    // Store the collision response and reset the player velocity
    %collision = $pNinja.castCollision(0.005);
    $pNinja.setLinearVelocityY(%yVel);
    
    if(%collision $= "")
    {
        // If there's no collision we need to turn on gravity
        $pNinja.setConstantForceY(100);
    }
    else
    {
        // otherwise turn it off.
        $pNinja.setConstantForceY(0);
    }
}

function t2dscenegraph::onUpdateScene()
{
     $pNinja.updateMovement();
}