Show your built archive structure, especially the location of jars. Most probably you have two jboss-seam.jars.
If you use Maven, be aware that when adding jboss-seam-debug or jboss-seam-ui dependencies to your web project, it also adds the jboss-seam transitive dependency while it is already present in ear. If this is your case, you will have to add an exclusion in pom.xml file :
<dependency> <groupId>org.jboss.seam</groupId> <artifactId>jboss-seam-ui</artifactId> <exclusions> <exclusion> <groupId>org.jboss.seam</groupId> <artifactId>jboss-seam</artifactId> </exclusion> </exclusions> </dependency>