<span id="<%=ClientID %>_MouseXY">failed</span>

        protected void Page_Load(object sender, EventArgs e)
        {
            Page.ClientScript.RegisterClientScriptBlock(GetType(),"BitlinkMouseXY",@"
            $(function (){
            $('#" + ClientID + @"_MouseXY').html('worked');
            });", true);
        }


$(document).ready(function (){
// code
});

Becomes (in JQuery)

$(function (){
// code
});