Well, since the stack trace refers to
DTD, I'd guess that it's not able to fetch the DTD from the hibernate site in order to do validation - you are referencing an external DTD in your xml file.
Quote:
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:626)
at org.apache.xerces.impl.XMLEntityManager.setupCurrentEntity(Unknown Source)
at org.apache.xerces.impl.XMLEntityManager.startEntity(Unknown Source)
at org.apache.xerces.impl.XMLEntityManager.startDTDEntity(Unknown Source)
at org.apache.xerces.impl.XMLDTDScannerImpl.setInputSource(Unknown Source)
at org.apache.xerces.impl.XMLDocumentScannerImpl$DTDDispatcher.dispatch(Unknown Source)