为什么会“缺少对象”

<asp:ScriptManager ID="ScriptManager1" runat="server">
    </asp:ScriptManager>
    <script language ="javascript" type ="text/jscript" >
   Type.registerNamespace ("person");
   person.head=function (count)
   {
     this._count=count ;
   }
   person.head.prototype=
   {
    get_headCount:function ()
    {
     return this._count;
    }   
   }
   person.head.regisiterClass("person.head",null);
   
   person.Employe = function(count,title)
{
this._title = title;
}
person.Employe.prototype = 
{
get_title : function()
{
return this._title;
}

}
person.Employe.registerClass("person.Employe", null);    </script>
     <input id="Button1" type="button" value="显示结果" onclick="alert(new person.Employe('big','2'));" />