The class loader used by coherence should also look up in the other plugins. ClassLoader: org.jivesoftware.openfire.container.PluginClassLoader@199c2e java.io.IOException: readObject failed: java.lang.ClassNotFoundException: org.jivesoftware.openfire.gateway.registration.cluster.SeniorRegistrationRequest at java.net.URLClassLoader$1.run(URLClassLoader.java:200) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:188) at java.lang.ClassLoader.loadClass(ClassLoader.java:306) at java.lang.ClassLoader.loadClass(ClassLoader.java:251) at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319) at java.lang.Class.forName0(Native Method) at java.lang.Class.forName(Class.java:242) at java.io.ObjectInputStream.resolveClass(ObjectInputStream.java:585) at com.tangosol.io.ResolvingObjectInputStream.resolveClass(ResolvingObjectInputStream.java:68) at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1544) at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1466) at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1699) at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1305) at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1908) at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1832) at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1719) at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1305) at java.io.ObjectInputStream.readObject(ObjectInputStream.java:348) at com.tangosol.util.ExternalizableHelper.readSerializable(ExternalizableHelper.java:2084) at com.tangosol.util.ExternalizableHelper.readObject(ExternalizableHelper.java:2202) at com.tangosol.coherence.component.net.Message.readObject(Message.CDB:3) at com.tangosol.coherence.component.util.daemon.queueProcessor.service.InvocationService$InvocationRequest.read(InvocationService.CDB:8) at com.tangosol.coherence.component.util.daemon.queueProcessor.Service.onNotify(Service.CDB:110) at com.tangosol.coherence.component.util.Daemon.run(Daemon.CDB:35) at java.lang.Thread.run(Thread.java:613)