Modal Popup extender

I am trying to show and hide a modal popup in auser control which is called under contentpage of masterpage , as aseparate page the sample works fine but when embed this sample in usercontrol or content page or master page i get the error say this._popupis null or not an object

The following is the code
<script type="text/javascript" language="javascript">
var _popup;

function validate(){
// find the popup behavior
this._popup = $find('mdlPopup');
// show the popup
this._popup.show();
// kick-off the webservice, registering our callback
PageMethods.ValidateCreditCard($get('txtNumber').value, this.callback);
}

function callback(result){
// hide the popup
this._popup.hide();

// let the user know if their credit card was validated
if(result){
alert('congrats, your Number is valid!');
}
else{
alert('sorry, your Number is not valid!');
}
}

</script>
<script runat="server">
/// <summary>
///
/// </summary>
/// <param name="number"></param>
/// <returns></returns>
[System.Web.Services.WebMethod]
public static bool ValidateNumber(string Number)
{

bool isValid = false;
try
{

if(Number=="234")
{
isValid=true;
}

}
catch {}

return isValid;
}
</script>

Thanks

Are you using the $find command correctly? See the documentation:http://www.asp.net/ajax/documentation/live/ClientReference/Sys/ApplicationClass/SysApplicationFindComponentMethod.aspx.

It states "Use the findComponent method to get a reference to a Component object that has been registered with the application through theaddComponent method.".

Also, your problem could be that the client ID isn't 'mdlPopup' since it is a apart of a container control.

-Damien