JBoss AS already provides the JSF JAR files, so including them in your WAR will cause problems. You need to ensure that the WAR does nto contain the JSF JAR files.
For your post, I suspect that you are using an IDE. Which one? If NetBeans, I don't know how to convince it to use a JAR file during the compile but not package it in the WAR for deployment. For Eclipse, I recommend using JBoss Tools also - it knows how to properly package WARs for deployment to JBoss AS.
first let me thank for your answer.
I finally solved the problem. I still include the jsf jars as Library but uncheck the "package" checkbox so the files are not packed in the war file.
Is this now the correct solution?