Hi when you use master page control then server control of childpage need to be identified by its CLientID
so in stead of using id of control in javascript file better that you should use that control's clientID.
$("#<%txtSearch.ClientID%>").bind("keydown", function (event) {
if (event.keyCode === $.ui.keyCode.TAB &&
$(this).data("autocomplete").menu.active) {
event.preventDefault();
}
})