Error

I have the following AS in place in a frame:


import mx.transitions.Tween;
import mx.transitions.easing.*;

this.mainpage_btn_mc.onRelease = function(){
	mainpage_btn_mc.gotoAndPlay("_down");
    new Tween(work_btn_mc, "_y", None, 43.5, 100, 12, false);
}

But I get the following error:

**Error** Symbol=Nav_mc, layer=constants, frame=1:Line 12: Operator '=' must be followed by an operand
         new Tween(work_btn_mc, "_y", None, 43.5, 100, 12, false);

**Error** Symbol=Nav_mc, layer=constants, frame=1:Line 13: Unexpected '}' encountered
     }

Total ActionScript Errors: 2 	 Reported Errors: 2

What am I doing wrong?