Caused by: java.lang.ClassNotFoundException: org.jboss.ejb3.singleton.proxy.impl.invocationhandler.SingletonBeanRemoteInvocationHandler (no security manager: RMI class loader disabled)
You'll require the jbossall-client.jar (and all the other jars referenced in its META-INF/MANIFEST.MF file) in the client's classpath. These jars should be the same as the ones that are there in the JBOSS_HOME/client folder of JBoss AS 6.0.0.M3