PHP issue with XML/DOMDocument

The following code is having issues, will paste error below:

<?php

$xmlwithdtd = "    <?xml version=\"1.0\" encoding=\"utf-8\" ?><!DOCTYPE REQUEST [
    <!ELEMENT REQUEST (COMMUNICATION_CODE,PARTNER_ID,SID)>
    <!ELEMENT COMMUNICATION_CODE (#PCDATA)>
    <!ELEMENT PARTNER_ID (#PCDATA)>
    <!ELEMENT SID (#PCDATA)>
    ]>
    <REQUEST>
  <COMMUNICATION_CODE>FAR001</COMMUNICATION_CODE>
  <PARTNER_ID>LL-236021118-1</PARTNER_ID>
  <SID>YourLimeLockSessionID</SID>
</REQUEST>";        

        $dom = new DOMDocument;
        $dom->Load($xmlwithdtd);
        if ($dom->validate()) {
            echo "valid";    
        } else {
            echo "not valid";
        }
?>  

Error:


Warning: DOMDocument::load() [domdocument.load]: I/O warning : failed to load external entity "/Applications/MAMP/htdocs/testzone/%20%20%20%20%3C%3Fxml%20version=%221.0%22%20encoding=%22utf-8%22%20%3F%3E%3C!DOCTYPE%20REQUEST%20%5B%0A%20%20%20%20%3C!ELEMENT%20REQUEST%20(COMMUNICATION_CODE,PARTNER_ID,SID)%3E%20%0A%20%20%20%20%3C!ELEMENT%20COMMUNICATION_CODE%20(%23PCDATA)%3E%20%0A%20%20%20%20%3C!ELEMENT%20PARTNER_ID%20(%23PCDATA)%3E%0A%20%20%20%20%3C!ELEMENT%20SID%20(%23PCDATA)%3E%0A%20%20%20%20%5D%3E%0A%20%20%20%20%3CREQUEST%3E%0A%20%20%3CCOMMUNICATION_CODE%3EFAR001%3C/COMMUNICATION_CODE%3E%0A%20%20%3CPARTNER_ID%3ELL-236021118-1%3C/PARTNER_ID%3E%0A%20%20%3CSID%3EYourLimeLockSessionID%3C/SID%3E%0A%3C/REQUEST%3E" in /Applications/MAMP/htdocs/testzone/foo.php on line 16

Warning: DOMDocument::validate() [domdocument.validate]: no DTD found! in /Applications/MAMP/htdocs/testzone/foo.php on line 17
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