At the time of writing, it was Scala 2.10.0-M7 and Akka 2.1-M2. When everything finally solidifies, I'll be switching it to 2.10.0 and 2.1 proper. You should be able to use 2.10.0-RC1 and 2.1-RC1 and have no issues.
But, I think you're just missing the pattern import.
and you should get the '?' method added on to the ActorRef.