In akka-microkernel 1.2 RC6 there two versions (2.3.0 and 2.4.1) of protobuf-java present in the lib directory. In akka-core, there is only 2.4.1. Presence of 2.3.0 in microkernel distribution causes exceptions when trying to send message to remote actors. Reproducible case is the minimal remote example at https://github.com/jboner/akka/tree/master/akka-samples/akka-sample-remote .

Exception stack trace from my project:

java.lang.NoSuchFieldError: alwaysUseFieldBuilders 
        at akka.remote.protocol.RemoteProtocol$UuidProtocol.access 
$13100(RemoteProtocol.java:8419) 
        at akka.remote.protocol.RemoteProtocol$UuidProtocol 
$Builder.maybeForceBuilderInitialization(RemoteProtocol.java:8630) 
        at akka.remote.protocol.RemoteProtocol$UuidProtocol 
$Builder.<init>(RemoteProtocol.java:8622) 
        at akka.remote.protocol.RemoteProtocol$UuidProtocol 
$Builder.create(RemoteProtocol.java:8634) 
        at akka.remote.protocol.RemoteProtocol$UuidProtocol$Builder.access 
$12900(RemoteProtocol.java:8607) 
        at akka.remote.protocol.RemoteProtocol 
$UuidProtocol.newBuilder(RemoteProtocol.java:8594) 
        at akka.serialization.RemoteActorSerialization 
$.createRemoteMessageProtocolBuilder(SerializationProtocol.scala:294) 
        at akka.remote.netty.RemoteClient.send(NettyRemoteSupport.scala:235) 
        at akka.remote.netty.NettyRemoteClientModule$$anonfun$send 
$1.apply(NettyRemoteSupport.scala:94) 
        at akka.remote.netty.NettyRemoteClientModule$$anonfun$send 
$1.apply(NettyRemoteSupport.scala:94) 
        at akka.remote.netty.NettyRemoteClientModule 
$class.withClientFor(NettyRemoteSupport.scala:119) 
        at 
akka.remote.netty.NettyRemoteSupport.withClientFor(NettyRemoteSupport.scala : 
649) 
        at akka.remote.netty.NettyRemoteClientModule 
$class.send(NettyRemoteSupport.scala:94) 
        at akka.remote.netty.NettyRemoteSupport.send(NettyRemoteSupport.scala: 
649) 
        at akka.actor.RemoteActorRef.postMessageToMailbox(ActorRef.scala: 
1234) 
        at akka.actor.ScalaActorRef$class.$bang(ActorRef.scala:1400) 
        at akka.actor.RemoteActorRef.$bang(ActorRef.scala:1207) 
        at motifs.actors.NodeMaster.preStart(motifs-actors.scala:85) 
        at akka.actor.LocalActorRef.akka$actor$LocalActorRef$ 
$initializeActorInstance(ActorRef.scala:1173) 
        at akka.actor.LocalActorRef$$anonfun$start$1.apply(ActorRef.scala: 
704) 
        at akka.actor.LocalActorRef$$anonfun$start$1.apply(ActorRef.scala: 
694) 
        at akka.util.ReentrantGuard.withGuard(LockUtil.scala:20) 
        at akka.actor.LocalActorRef.start(ActorRef.scala:694) 
        at akka.actor.LocalActorRef.start(ActorRef.scala:605) 
        at Main$.main(motifs-run.scala:106) 
        at Main.main(motifs-run.scala) 
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 
        at 
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java: 
39) 
        at 
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImp l.java: 
25) 
        at java.lang.reflect.Method.invoke(Method.java:597) 
        at scala.tools.nsc.util.ScalaClassLoader$$anonfun$run 
$1.apply(ScalaClassLoader.scala:78) 
        at scala.tools.nsc.util.ScalaClassLoader 
$class.asContext(ScalaClassLoader.scala:24) 
        at scala.tools.nsc.util.ScalaClassLoader 
$URLClassLoader.asContext(ScalaClassLoader.scala:88) 
        at scala.tools.nsc.util.ScalaClassLoader 
$class.run(ScalaClassLoader.scala:78) 
        at scala.tools.nsc.util.ScalaClassLoader 
$URLClassLoader.run(ScalaClassLoader.scala:101) 
        at scala.tools.nsc.ObjectRunner$.run(ObjectRunner.scala:33) 
        at scala.tools.nsc.ObjectRunner$.runAndCatch(ObjectRunner.scala:40) 
        at scala.tools.nsc.ScriptRunner.scala$tools$nsc$ScriptRunner$ 
$runCompiled(ScriptRunner.scala:180) 
        at scala.tools.nsc.ScriptRunner$$anonfun$runScript 
$1.apply(ScriptRunner.scala:197) 
        at scala.tools.nsc.ScriptRunner$$anonfun$runScript 
$1.apply(ScriptRunner.scala:197) 
        at scala.tools.nsc.ScriptRunner$$anonfun$withCompiledScript$1$$anonfun 
$apply$mcZ$sp$1.apply(ScriptRunner.scala:166) 
        at scala.tools.nsc.ScriptRunner$$anonfun$withCompiledScript$1$$anonfun 
$apply$mcZ$sp$1.apply(ScriptRunner.scala:166) 
        at scala.Option.exists(Option.scala:188) 
        at scala.tools.nsc.ScriptRunner$$anonfun$withCompiledScript$1.apply 
$mcZ$sp(ScriptRunner.scala:166) 
        at scala.tools.nsc.ScriptRunner$$anonfun$withCompiledScript 
$1.apply(ScriptRunner.scala:140) 
        at scala.tools.nsc.ScriptRunner$$anonfun$withCompiledScript 
$1.apply(ScriptRunner.scala:140) 
        at scala.tools.nsc.util.package$.waitingForThreads(package.scala:26) 
        at scala.tools.nsc.ScriptRunner.withCompiledScript(ScriptRunner.scala: 
139) 
        at scala.tools.nsc.ScriptRunner.runScript(ScriptRunner.scala:197) 
        at scala.tools.nsc.ScriptRunner.runScriptAndCatch(ScriptRunner.scala: 
210) 
        at scala.tools.nsc.MainGenericRunner.runTarget 
$1(MainGenericRunner.scala:58) 
        at scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala: 
80) 
        at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala: 
89) 
        at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)