If you are working with JSF 2.0 there is a important change concerning the JSF core tags (<c:….>). These tags will not work if you are using the following namespace declaration:
<ui:composition xmlns="http://www.w3.org/1999/xhtml" xmlns:ui="http://java.sun.com/jsf/facelets" xmlns:f="http://java.sun.com/jsf/core" xmlns:c="http://java.sun.com/jstl/core" xmlns:h="http://java.sun.com/jsf/html">
This works in JSF 1.2 but well, but did no longer work in JSF 2.0. The reason is that the namespace uri for the jstl/core has changed. Use the following namespace definition if you are working with jsf 2.0
<ui:composition xmlns="http://www.w3.org/1999/xhtml" xmlns:ui="http://java.sun.com/jsf/facelets" xmlns:f="http://java.sun.com/jsf/core" xmlns:c="http://java.sun.com/jsp/jstl/core" xmlns:h="http://java.sun.com/jsf/html">