I got runtime script error

When i click the button in aspx page, it stops @ throw error line and cannot process further.

function Sys$WebForms$PageRequestManager$_endPostBack(error, executor, data) {
if (this._request === executor.get_webRequest()) {
this._processingRequest = false;
this._additionalInput = null;
this._request = null;
}
var handler = this._get_eventHandlerList().getHandler("endRequest");
var errorHandled = false;
if (handler) {
var eventArgs = new Sys.WebForms.EndRequestEventArgs(error, data ? data.dataItems : {}, executor);
handler(this, eventArgs);
errorHandled = eventArgs.get_errorHandled();
}
if (error && !errorHandled) {
throw error;
}
}


My ASPX contains this script:
-------------------------------
<script>
$(function() {
afterLoad();
});

function afterLoad() {
$( ".DatePicker" ).datepicker({defaultDate: '',dateFormat:'dd/mm/yy'});

$(window).resize(function() {
$('.searchContent').height($(this).height() - $('.searchPanel').height() - $('.menuWrapper').height());
});
$('.searchContent').height($(this).height() - $('.searchPanel').height() - $('.menuWrapper').height());
$('.tablePanel').each(function (i) {
$(this).scroll(function() {
$.cookie('panelH'+i,$(this).scrollLeft());
$.cookie('panelT'+i,$(this).scrollTop());
})

$(this).scrollLeft($.cookie('panelH'+i));
$(this).scrollTop($.cookie('panelT'+i));
})

$("#ctl00_ContentPlaceHolder2_InsertBtn").click(function () {
return confirm('Do you really want to get a new Contract No?');
});

$($(".ContractPeriod tr")[0]).hide();
$($(".CustomerTypePlan tr")[0]).hide();
$($(".CustomerTypePlan tr")[1]).hide();
//$(".TermsCondition").hide();

if ($(".IsPurchase input[checked='checked']").val() == "True") {
$($(".ContractPeriod tr")[1]).show();
$($(".CustomerTypePlan tr")[2]).show();
$($(".CustomerTypePlan tr")[3]).hide();
$($(".CustomerTypePlan tr")[4]).hide();
$($(".CustomerTypePlan tr")[5]).hide();
$($(".CustomerTypePlan tr")[6]).hide();

} else {
/*$($(".ContractPeriod tr")[1]).hide();*/
$($(".CustomerTypePlan tr")[2]).hide();
$($(".CustomerTypePlan tr")[3]).show();
$($(".CustomerTypePlan tr")[4]).show();
$($(".CustomerTypePlan tr")[5]).show();
$($(".CustomerTypePlan tr")[6]).show();
}
}
</script>


If i click the button, i didn't get the confirmation dialog box(written in above script block).