The ExceptionHandler is used to clean Seam contexts and transactions after errors.

      <context-param>
         <param-name>org.jboss.portletbridge.ExceptionHandler</param-name>
         <param-value>
            org.jboss.portletbridge.SeamExceptionHandlerImpl
         </param-value>
      </context-param>
      

There is workaround for Seam 2.0.0/2.0.1 distributions. This is not needed for Seam 2.1.x releases.

      <context-param>
        <param-name>javax.faces.LIFECYCLE_ID</param-name>
        <param-value>SEAM_PORTLET</param-value>
      </context-param>