Seeing the same "error firing server event" message when deploying ESB files or importing the helloworld project example (per JBDS-1356)... This may be similar to JBIDE-3502 which was closed back in 3.0

!ENTRY org.eclipse.wst.server.core 4 0 2010-10-06 12:12:53.424
!MESSAGE Error firing server event: org.jboss.ide.eclipse.as.core.server.UnitedServerListenerManager@1ec1774
!STACK 0
java.util.ConcurrentModificationException
at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:782)
at java.util.ArrayList$Itr.next(ArrayList.java:754)
at org.jboss.ide.eclipse.as.core.server.UnitedServerListenerManager.serverChanged(UnitedServerListenerManager.java:131)
at org.eclipse.wst.server.core.internal.ServerNotificationManager.broadcastChange(ServerNotificationManager.java:110)
at org.eclipse.wst.server.core.internal.Server.fireServerStateChangeEvent(Server.java:691)
at org.eclipse.wst.server.core.internal.Server.setServerState(Server.java:628)
at org.eclipse.wst.server.core.model.ServerBehaviourDelegate.setServerState(ServerBehaviourDelegate.java:144)
at org.jboss.ide.eclipse.as.core.server.internal.DeployableServerBehavior.setServerStarted(DeployableServerBehavior.java:131)
at org.jboss.ide.eclipse.as.core.server.internal.PollThread.alertBehavior(PollThread.java:226)
at org.jboss.ide.eclipse.as.core.server.internal.PollThread.run(PollThread.java:177)