flash error 1010 when trying to snap a puzzle piece
===

i am trying to create a puzzle game and so far had no problems with moving the pieces and all but when i tried to check piece position after stopDrag i got an error message:Error #1010: A term is undefined and has no properties.

this is the relevant code:
full1 is a movieclip that contains a picture of the puzzle with a low alpha and the puzzle pieces,each with it's own instance name.
in this example tr is an instance name of one of the pieces. 

    	public function Move(even:MouseEvent)
    {
    	even.target.startDrag();
    		
    }
    	public function stopMove(even:MouseEvent)
    {
    	this.stopDrag();
    	checkPos(even.target.name);
    		
    }
    	public function checkPos(nameStr:String)
    {
    
    	if(nameStr=="tr1")
    	{
    		if(this.full1.tr1.x>=460&&this.full1.tr1.x<=465.5&&this.full1.tr.y>=99&&this.full1.tr.y<=103)
    		{
    			this.full1.tr.x=460.2;
    			this.full1.tr.y=101.95;
    		}
    	}
    
    	
    		
    }

if anyone sees any problem with what i wrote or has a better idea of how to approach this i would appreciate your help.
thanks.
