The error could indicate many different things. Are you absolutely certain the XML is valid? Can you move the XML from that resource, place it in a local folder, and then point your code to that local folder/file? If so, does the code work then?
If it does, that would indicate troubles with the location hosting your file.
If it does not, that would indicate trouble with your code (although I'd think not, since you can point your code to a different XML file and all works).