Error while finding object's index in an array

[onurcan1977]

I've an array with some properties. When I try to find an object's index I'm getting error TypeError: Error #1009. I'm using Flash CS6.

Here's my array:

var squareArr:Object  = {
     a1: {
          piece: wr1_txt,
          pieceLoc: {  
            x: "-3",
            y: "347"
          }
     },
     b1: {
          piece: wn1_txt,
          pieceLoc: {  
            x: "47",
            y: "347"
          }
     },
...

Below code is giving me error #1009 while I want it to return a1:

trace (squareArr.indexOf(wr1_txt));

I tried:

var s:String;
var found:Boolean=false;
for (s in squareArr) {
    if (squareArr[s].piece == wr1_txt) { // YAY found it
        found=true;
        break;
    }
}
if (found) trace(s); else trace("Not found!");

but it says not found