If you use the JBoss application server, you must customize the web.xml file in the Alfresco ROOT.war, _vti_bin.war and share.war files to include this code fragment:
<context-param>
<param-name>
org.jboss.jbossfaces.WAR_BUNDLES_JSF_IMPL
</param-name>
<param-value>true</param-value>
</context-param>
This ensures that the JSF deployer in JBoss uses its own bundled JSF version.