responseXML returns null

[plits]

I created my first AJAX application and everything was going great when I used responseText to retrieve my data.

I decided to switch to XML output and now I receive "Object Null" error when I alert my output. When I change it back to responseText I can see the XML output.

Can someone tell me what is wrong?

function stateChanged() 
{ 
  if ((xmlRT.readyState==4)&&(xmlRT.status == 200))
  { 
    var xmlobj=xmlRT.responseXML;
    alert(xmlobj);
   }
} 

[Jordan]

There can be several reasons for this but one of the most common is that the content you are reading is not set to text/html.

In PHP you set it:

header("Content-type: text/xml"); 

An easy way to tell is to load your output into your browser. It should appear in XML format (with a tree like structure) and not just plain text.