Javascript Dialog Checkbox Undefined

I have a form with javascript and I'm trying to add a checkbox to a dialog, but it always returns undefined. The first checkbox works fine, but I cannot figure out why the second one with id "ckbox2" doesn't.  The alert says it's undefined so it never goes into the if statement. I didn't write this code, I'm just trying to add the checkbox, but I don't see where it's wrong, any help is appreciated.

Here's the snippet:

function f_getCheck()
{
if(this.getField("numCks").value>9){app.alert("You may only include ten items in a deposit with a hold!");end;}
var y = this.getField("numCks").value;
var z = this.getField("t_Code."+ y).value;
if(z=="E"){f_getCkReason()};
var dialog8 = {
	initialize: function(dialog){
		this.test1 = "";
		this.test2 = "";
},
	validate: function(dialog){
		var val = dialog.store();
		this.test1 = val["rtno"];
		this.test2 = val["iamt"] * 1;
		if(this.test1.length==9&&(this.test1*1)>0&&this.test2>0){
		fcb_ABA(this.test1, this.test2);
		} else {
		app.alert("Routing Numbers must be nine digits and amounts must be greater than zero");
		return false};
		return true;
	},
	commit: function(dialog){
		var results=dialog.store();
		this.RTNum = results["rtno"];
		this.Amt = results["iamt"];
		this.ExCkHold = results["ckbx"];
		this.RetCk = results["ckbox2"];
		app.alert(this.RetCk);
	},
	ok: function(dialog){
		var results=dialog.store();
		dialog.end("ok");

	},

	cancel: function(dialog){
		var results=dialog.store();
		dialog.end("del");

	},
	other: function(dialog){
		var results=dialog.store();
		dialog.end("done");
	},

	loadDefaults: function(dialog){},
	description: {
		name: "Check Entry",
		elements: [{
			type: "view",
			align_children: "align_left",
			elements:[{
				type: "cluster",
				name: "Enter the information for the check.",
				align_children: "align_row",
				elements:[{
					type:"view",
					align_children:"align_left",
					elements:[{
    						type:"static_text",
						name:"Routing/Transit Number"},
						{item_id:"rtno",
						type:"edit_text",
						char_width: 9}
					]},
					{type:"view",
					align_children:"align_left",
					elements:[{
						type:"static_text",
						name:"Amount of item (xxxx.xx)"},
						{item_id:"iamt",
						type:"edit_text",
						char_width: 12}]}]},
						{type:"check_box",
						item_id: "ckbx",
						name: "Check here to exclude from amount on hold and deposit information."},
						{type: "check_box",
						item_id: "ckbx2",
						name: "Check here if this is an Exempt item."},
						{type: "static_text",
						name: "Exempt items include items drawn on state, local, U.S. governments, cashier's checks, and the like.",
						italics:true},
						{type: "ok_cancel_other",
						ok_name: "Add check to deposit",
						cancel_name: "Delete an item",
						other_name: "No more items"}]}]}};

var myResult = app.execDialog(dialog8);
if(myResult=="done"){f_AllDone()};
if(myResult=="cancel"){f_delItems()};
if(myResult=="ok"){
	if(dialog8.ExCkHold==true){
		this.getField("t_Code."+(this.getField("numCks").value-1)).value = "";
		this.getField("ExType."+(this.getField("numCks").value-1)).value="";
		this.getField("RT."+(this.getField("numCks").value-1)).value="";
		this.getField("ckAmt."+(this.getField("numCks").value-1)).value="";
		this.getField("numCks").value--;
	}
	else {
		if(dialog8.RetCk==true){
		this.getField("ExType." + (this.getField("numCks").value-1)).value = "-Exempt-\rOther";
		var xx = this.getField("numCks").value*1-1;
		var xxx = this.getField("t_Code." + xx).value;
		if(xxx=="A"){} else {this.getField("t_Code." + (this.getField("numCks").value-1)).value = "-"};
		if(xxx=="F"){this.getField("t_Code." + (this.getField("numCks").value-1)).value = "F"}
		};
	};
	f_getCheck()
};
}