The first line is not supported on the Cisco SIP IP Phone. Therefore, deleting this line should resolve the issue.
Make sure that the XML file cannot be directly requested in a URL. Instead, point it to a Common Gateway Interface (CGI) like a Practical Extraction and Reporting Language (PERL) or Active Server Page (ASP) script and have the CGI do this job. The reason behind this is that some HTTP headers need to be set from the CGI instead of using the default chosen by the HTTP server.