The solution is here
I copy the solution from the link above
make sure that you do not have the same library twice.
I got the same error, because I had 2 different versions of the same library (jsf-impl.jar):
* one in my .war archive under WEB-INF/lib
* the other one in jboss-4.2.0.GA\server\default\deploy\jboss-web.deployer\jsf-libs
removing the library from my .war archive fixed it
I have prove this solution with my problem and I have resolved