After creating a new Seam project via the wizard (EAR packaging, configuration "Dynamic Web project with Seam 2.0"), starting up JBoss produces the following error:

duplicate factory for: org.jboss.seam.web.webSession (duplicate is specified in components.xml)

Even after removing jboss-seam.jar from the war MANIFEST.INF as suggested here (http://www.seamframework.org/Community/HowToUpdateProjectFrom20To21Seam) the error still occurs.

This is the only other reference that I've found to this error (http://jira.jboss.com/jira/browse/JBSEAM-2981) but it looks slightly unrelated to me.

Stack trace:
19:05:32,116 ERROR [[/hellome]] Excepción enviando evento inicializado de contexto a instancia de escuchador de clase org.jboss.seam.servlet.SeamListener
java.lang.IllegalStateException: duplicate factory for: org.jboss.seam.web.webSession (duplicate is specified in components.xml)
at org.jboss.seam.core.Init.checkDuplicateFactoryExpressions(Init.java:222)
at org.jboss.seam.core.Init.checkDuplicateFactory(Init.java:215)
at org.jboss.seam.core.Init.addFactoryValueExpression(Init.java:278)
at org.jboss.seam.init.Initialization.installComponents(Initialization.java:983)
at org.jboss.seam.init.Initialization.init(Initialization.java:631)
at org.jboss.seam.servlet.SeamListener.contextInitialized(SeamListener.java:34)
at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:3856)
at org.apache.catalina.core.StandardContext.start(StandardContext.java:4361)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:790)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:770)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:553)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
....

I believe also these others warnings might be related to the same problem (which i suspect is duplicate jar in the classpath of the war):

19:49:24,506 INFO [TomcatDeployer] deploy, ctxPath=/jmx-console, warUrl=.../deploy/jmx-console.war/
19:49:25,506 INFO [EARDeployer] Init J2EE application: file:/D:/Java/jboss-4.2.3.GA/server/default/deploy/hellome-ear.ear/
19:49:35,459 WARN [MainDeployer] Found non-jar deployer for jboss-seam.jar: MBeanProxyExt[jboss.ejb3:service=EJB3Deployer]
19:49:42,381 WARN [DeploymentInfo] Only the root deployment can set the loader repository, ignoring config=LoaderRepositoryConfig(repositoryName: seam.jboss.org:loader=hellome, repositoryClassName: org.jboss.mx.loading.HeirarchicalLoaderRepository3, configParserClassName: org.jboss.mx.loading.HeirarchicalLoaderRepository3ConfigParser, repositoryConfig: java2ParentDelegation=false)
19:50:00,679 INFO [JmxKernelAbstraction] creating wrapper delegate for: org.jboss.ejb3.entity.PersistenceUnitDeployment

19:50:04,976 INFO [TomcatDeployer] deploy, ctxPath=/hellome, warUrl=.../deploy/hellome-ear.ear/hellome.war/
19:50:13,554 WARN [SeamPhaseListener] There should only be one Seam phase listener per application
19:50:20,726 INFO [ServletContextListener] Welcome to Seam 2.1.0.BETA1