I have an issue with a SharePoint 2010 xml viewer webpart and an xml feed that contains DOCTYPE.
The xml renders fine when there is no associated XSL with the webpart. When I add XSL to the webpart I receive the following error: "Failed to apply XSLT to the content". I discovered that if I remove the
<!DOCTYPE NewsML PUBLIC "+//W3C//DTD NewsML 1.0//EN" "http://www.irxml.org/dtd/NewsML_1.0.dtd"> element from the XML it will render just fine with the XSL.