Hi, Vijendra Babar,
I guess that the problem comes from the version of the JBoss AS that you are using. The JEMS installer for JBoss AS 4.0.4 is required for using Seam (instead of the normal jboss-4.0.4.GA-Patch1-installer.jar).
You can read it in the getting started document:
( http://labs.jboss.com/portal/jbossseam/gettingstarted/index.html )
"Download the JEMS installer for JBoss AS 4.0.4 and install it with the EJB 3.0 profile selected. Note: do not install any other version of JBoss, and do not try to install JBoss using the normal JBoss AS installer - Seam requires EJB 3.0 RC8 which is only currently available in the special JEMS Installer!"
I had the same problem and the JEMS installer worked for me. I hope that this information will help you.