Please explain this error

1

Error Scene=Scene 1, layer=a, frame=1:Line 135: There is no method with the name ‘attachMovie’.
var btnOrg:MovieClip = (ob.attachMovie (“yelBtn”, “yt”, +i, i));
Total ActionScript Errors: 1 Reported Errors: 1

 
function myOnRollOver (id) {
 var boxNames = ["yb", "ob", "rb", "bb", "pb", "gb"];
 for (var i = 0; i < boxNames.length; i++) {
  var box = this[boxNames*];
  if (id == 0) {
   yelOnRollOver (box);
  }
  if (id == 1) {
   orgOnRollOver (box);
  }
  if (id == 2) {
   redOnRollOver (box);
  }
  if (id == 3) {
   pplOnRollOver (box);
  }
  else {
  }
 }
}
//Yellow Button
function yelOnRollOver () {
 var mcMenuTitles = ["yt", "ot", "rt", "bt", "pt", "gt"];
 for (var i = 0; i < mcMenuTitles.length; i++) {
  var titles = this[mcMenuTitles*];
  var yt:MovieClip = (yb.attachMovie ("yelBtn", "yt", +i, i));
  btnYel._width = yb._width;
  btnYel._y = yb._y;
  //Tween  
  new Tween (yt, "_alpha", Back.easeInOut, 0, 100, 1, true);
  new Tween (yt, "_y", Strong.easeOut, 0, 175, 3, true);
 }
 new Tween (yb, "_alpha", Back.easeInOut, 50, 125, 2, true);
}
//myBio Script
function myBio () {
 var myBlur:BlurFilter = new flash.filters.BlurFilter (25, 25, 2);
 var t1:Tween = new Tween (yb, "_x", Back.easeInOut, 100, 300, 2, true);
 var t3:Tween = new Tween (yb, "myBlur", Back.easeInOut, 0, 100, 1, true);
}
function orgOnRollOver () {
 for (var i = 0; i < 1; i++) {
  var btnOrg:MovieClip = (ob.attachMovie ("yelBtn", "yt", +i, i));
  orgBtn._width = ob._width;
  OrgBtn._y = ob._y;
  //Tween  
  new Tween (orgBtn, "_alpha", Back.easeInOut, 0, 100, 2, true);
  new Tween (orgBtn, "_y", Bounce.easeOut, 0, 175, 4, true);
 }
 new Tween (ob, "_alpha", Back.easeInOut, 50, 125, 2, true);
}