DOM Version Mismatch Test in IE

I'm trying to load a document in IE6 and copy nodes from one document tree to another. The information is accessible, but the copy fails with the error No such interface supported (-214746262). According to the support pages this could be a mismatch between the versions of the DOM being used.

function Callback(request, objectID) {
  this.callback.request = request;
  this.callback.objectID = objectID;
  request.onreadystatechange = this.callback;
  try {
    request.open("GET", window.location.pathname.replace(/\.[^\.]+$/, ".xml"));
    request.send(null);
  } catch(e) {
    debug("For: \"" + objectID + "\": " + e);
  }
}
Callback.prototype = new Object;
Callback.prototype.callback = function() {
  var request = arguments.callee.request;
  if(request.readyState == 4 && request.status == 200) {
    if(request.responseXML.parseError && request.responseXML.parseError != 0) {
      debug("Parse Error Loading HTML: " + 
            request.responseXML.parseError + 
            " (" + request.responseXML.parseError.srcText + ")");
    } else {
      var objectID = arguments.callee.objectID;
      debug("For object: " + objectID + " got document: " + request.responseXML);
      var loadedBody = selectNodes(request.responseXML, "//html:body", "html", "http://www.w3.org/1999/xhtml").item(0);
      debug("For object: " + objectID + " got body: " + loadedBody.nodeName);
      try {
        var holder = document.createElement("div");
        while(loadedBody.hasChildNodes()) {
          var child = loadedBody.firstChild;
          loadedBody.removeChild(child);
          holder.appendChild(request.responseXML.importNode(child, true));
          //holder.appendChild(child);
          //if(child.nodeType == Node.ELEMENT_NODE)
          //  holder.innerHTML += child.innerHTML;
        }
        holder.style.backgroundColor = "yellow";
        document.getElementsByTagName("body").item(0).appendChild(holder);
        debug("Loaded Successfully with: " + objectID + " nodes " + holder.childNodes.length);
      } catch(e) {
        debug(objectID + " failed: " + e.message + " (" + e.number + ")");
      }
    }
  }
}
if(typeof(XMLHttpRequest) != "undefined") {
  new Callback(new XMLHttpRequest(), "XMLHttpRequest");
}
if(window.ActiveXObject) {
  var msxmlProgids = new Array("MSXML2.XMLHTTP.5.0",
                               "MSXML2.XMLHTTP.4.0",
                               "MSXML2.XMLHTTP.3.0",
                               "MSXML2.XMLHTTP",
                               "Microsoft.XMLHTTP");
  for(var i = 0; i < msxmlProgids.length; i++) {
    try {
      new Callback(new ActiveXObject(msxmlProgids[i]), msxmlProgids[i]);
    } catch(e) {
      debug("Failed to Load: " + msxmlProgids[i]);
    }
  }
}