I'm using latest CVS Seam with Trinidad, Facelets 1.12 and Ajax4Jsf without getting the exception you're seeing. Set up your Ajax4Jsf filter mapping as follows: <filter-mapping> | <filter-name>ajax4jsf</filter-name> | <servlet-name>Faces Servlet</servlet-name> | <dispatcher>REQUEST</dispatcher> | <dispatcher>FORWARD</dispatcher> | <dispatcher>INCLUDE</dispatcher> | </filter-mapping> Does that make any difference? View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4049564#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...