LWP::UserAgent doesn't give a damn about that data or what kind of data the server sends. You get what the server sent so either you sent an invalid request and the script on the server produced an invalid response or there's an error on the server or you failed to read the docs and the response is just all right. In the last case if you need to parse the partial XML (missing the root tag), you can store it in a file and parse

  <!DOCTYPE doc [<!ENTITY real_doc SYSTEM "$the_file_name">]><doc>&rea
+l_doc;</doc>
[download]

instead.

(I see a "how do I save XML in a file" question coming ...)