uncaught exception: Missing instance data for this datepicker

Hi, I'm using vs2012.
My jQuery datepicker was working fine but something I did recently broke it in Firefox.  In IE and Chrome it's working just fine.  I get this error when I click on the cell in a Gridview control where the datepicker supposed to pop up but instead I would get this error in FireBug.  What does this mean and how to fix it?  Thank you.

    <script>
    $(document).ready(function () {
        Sys.WebForms.PageRequestManager.getInstance().add_endRequest(bindPicker);
        bindPicker();
    });
    function bindPicker() {      
            $("input[type=text][id*=txtExpDate]").datepicker();
    }
</script>