Unable To Load Xml File When Running In IE8,IE7?

i have a requirement like, i need to search the xml file using xpath expression.
for that, first i need to load the xml file into javascript function using the below line of code.

function loadXMLDoc(dname) {
if (window.XMLHttpRequest) { for ie 7+,all
xhttp = new XMLHttpRequest();
alert('entered in method--if');

[Code]....

i am able to load the xml file in all the browsers except IE7,IE8. i am getting an error as "ACCESS DENIED". and the error i am getting the error at line, xhttp.open("GET", dname, false);