When searching always receiving an Alert message and no results. The log shows an HTTP 500 error trying to retrieve http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd but I was able to download it just fine using my browser.
The problem is that w3 is blocking excessive requests to DTD's.
See for an explanation http://www.vineetmanohar.com/2010/11/w3-org-dtds-blocked-from-java-http-500/
DTD's should be stored locally and the XML parser should look locally for DTD's first.
Here is a patch to add an XML catalog and change the twinpeaks DomUtil parser to use the catalog.
I also noticed this gave a speed improvement since the DTD is local.