Got error Ajax manager is null in Master page

[M Kumar]

Hi sir

     I use RadAjaxManager in master page  i call the RadAjaxManager in master.js file. in Grid itemdatabound call the function

 

if (gridid.toString().toLowerCase().indexOf("explorergrid") >= 0) {
    $("#ContentPlaceHolder1_ExplorerGridSelectedIndexHidden").val(index);
    var ajaxManager = $find('ctl00_RadAjaxManager1');
    ajaxManager.ajaxRequestWithTarget('ctl00$ContentPlaceHolder1$explorerGridViewLink', '');
}

 

when click the grid i got the error in png