The Xtags fail to work when using the current version of Jaxen (jaxen-1.1-beta- 8). The reason seems to be the class org.jaxen.dom.DocumentNavigator, method getInstance(), which causes a NoSuchMethodException when the taglib tries to call it. In earlier versions this method returned org.jaxen.DocumentNavigator, but now it returns org.jaxen.Navigator.
Resolving. Taglib has been retired.