If Liferay is running in a JBoss container, you should not copy the JSF-impl.jar into the WAR. JBoss itself manages that.
Your actual problem sounds like a different situation, however. If you have an el-impl.jar file in your WAR, remove that. Neither JBoss nor Tomcat6 needs that, and it will interfere with the Tomcat internal copy of el-impl.jar
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