just make some changes in javascript-
make a function
<script>
function disableMe(me)
{
me.disabled=true;
return true;
}
</script>
and now change the line at page load as
btnClick.Attributes.Add("onclick", "disableMe(this)");
return true; statement is reason to call server side code if u write return false; or remove return statement the server side code will not execute.
--Pankaj