Ajax Model Popup and JS dropdownlist search conflict

Hi ,

Below is my code for dropdown search 

$(document).ready(function () {
Sys.WebForms.PageRequestManager.getInstance().add_endRequest(EndRequestHandler);
Sys.WebForms.PageRequestManager.getInstance().beginAsyncPostBack();
function EndRequestHandler(sender, args) {
$(".chzn-select").chosen(); $(".chzn-select-deselect").chosen({ allow_single_deselect: true });
}
});

After putting this code into my asp .net project my ajax model popup does not showing in my page.

What to do??