Concatenate problem

hi

I have two movieclips in stage named home,home_mc . I want when mouseover on “home” it will change some property of “home_mc”.But dont know how to write this code.I am trying like this…

import caurina.transitions.*;

home.addEventListener(MouseEvent.ROLL_OVER,over)
//home.addEventListener(MouseEvent.ROLL_OUT,out)
function over(e:MouseEvent):void
{
Tweener.addTween(e.target.name+"_mc",{alpha:.5});

}

but it is throwing— Error #1069: Property alpha not found on String and there is no default value.

Please help …how to fix this??
Thanks in advance