Try this
function EnableDisableControls(flag) {
var hdnChkBox = document.getElementById("hdnChkBox").value;
var chkCheckBox = document.getElementById(hdnChkBox);
var hdnTextBox = document.getElementById("hdnTextBox").value;
var txtTextBox = document.getElementById(hdnTextBox);
chkCheckBox.disabled = flag;
txtTextBox.disabled = flag;
}
Hope this helps.