XML to PDF convertor

Hi,
I am trying to convert an XML file using XSLT to a PDF. But i am getting errors in the transformation.
they are

Transforming...

[INFO] building formatting object tree

[INFO] setting up fonts

[ERROR] Unsupported element encountered: html (Namespace: default). Source context: unavailable

[ERROR] Expected XSL-FO (root, page-sequence, etc.), SVG (svg, rect, etc.) or elements from another supported language.

javax.xml.transform.TransformerException: java.lang.NullPointerException




and i am using the code


try {
driver.setOutputStream(out);

//Setup XSLT
TransformerFactory factory = TransformerFactory.newInstance();
Transformer transformer = factory.newTransformer(new StreamSource(xslt));

//Setup input for XSLT transformation
Source src = new StreamSource(xml);

//Resulting SAX events (the generated FO) must be piped through to FOP
Result res = new SAXResult(driver.getContentHandler());

//Start XSLT transformation and FOP processing
transformer.transform(src, res);


i skipped the definition part.

So please somebody tell me what might be the problem.