Do i need to redefine instance in a class?

hey
Lets say i have a circle [instance name = countyA]

and i have a separate actionscript file that sets it to true or false

public function showThink(county:MovieClip):void
{

        county.visible=true; 
     }

when i test this with showThink(countyA);

i get Access of undefined property countyA.

Do i need to redefine this in my actionscript?