Check your classpath and java.endorsed.dirs env property value; the jaxws provider above is trying to get a new instance of org.jboss.ws.core.jaxws.spi.ProviderImpl which is the JBossWS-Native jaxws provider, but I assume you properly installed jbossws-cxf, given you mentioned cxf before, right?
I just got back from a 2 week vacation, this is why it took me some time to reply
I do use cxf and I've installed jbossws-cxf-3.4.1.GA from http://www.jboss.org/jbossws/downloads/ but the problem is that it alters the jboss installation. I'm only writing a plugin for an application that resided on jboss and therefore I cannot change the jboss installation.
In fact after installing jbossws-cxf-3.4.1.GA the jboss threw some errors on startup...
Is there a way to use jbossws-cxf without changing the jboss installation?
As for the endorsed dir, do you suggest avoiding it in the jboss startup script?
JBossWS-CXF 3.4.1 is not meant for running on top of JBoss AS 5.1.0. That's most probably why the server is not booting. Try starting over from a vanilla 5.1.0 and installing jbossws-cxf 3.4.0 if you need for an update.
Yes, of course the installation change some files on the server (especially installing jbws-cxf on top of an AS that includes jbossws-native), that the reason of updating ;-)
The plugin is meant for using the stack that's available. Check the way the classpath it's build; generally speaking the java.endorsed.dirs setup influences the resolution of the jaxws provider. So if that's pointing to a dir containing jbossws-native libs, the plugin will end up trying to instanciate native jaxws implementation, etc.