Hi everyone, I am using ajax4jsf 1.1.1, seam 1.2.1 and jcifs1.2.17.jar with NtlmHttpFilter for single sign on capability. I was getting the famous "Stack must not be null" error : ERROR [ExceptionFilter] uncaught exception javax.servlet.ServletException: Stack must not be null at javax.faces.webapp.FacesServlet.service(FacesServlet.java:152) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter........... The error stopped showing when I removed SeamFilter and SeamRidirectFilter declarations from web.xml. Can anyone explain this weirdness? I don't truly understand how seam filters work, but I would expect them to exist in the seam application. Now my app has ajax filter, NtlmHttpFilter and seam exception filter. that is another thing, how come seam Exception filter does not cause a problem? Any ideas ? Thanks View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4089753#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...