Size limit when importing XML using window.XMLHttpRequest

Question

Trying to import a 400+ node XML file using window.XMLHttpRequest and it seems to break. If I cut the XML down to 100 nodes or so the function returns a value correctly.

function loadXMLDoc(dname)
{
if (window.XMLHttpRequest)
  {
  xhttp=new XMLHttpRequest();
  }
else
  {
  xhttp=new ActiveXObject("Microsoft.XMLHTTP");
  }
xhttp.open("GET",dname,false);
xhttp.send();
return xhttp.responseXML;
}

I've tried using "POST" and that doesn't seem to make any difference. Is it possible to do what I want or will I have to try another method.

Many thanks.