java.lang.NoSuchMethodError with Scala actors

I have a simple Scala application (taken from here) which I want to test. The whole project is compiled successfully with SBT. However, when I launch the tests with sbt test I get the following error message:

Could not run test ConnectionTest:java.lang.NoSuchMethodError: akka.actor.Props$.apply(Lscala/Function0;)Lakka/actor/Props;

From the internet search, I get the impression that some of my versioning is not compatible but that is merely a guess. What may be wrong?

[Test Case]

import akka.actor.{Props, Actor, ActorSystem, ActorRef}
import akka.testkit.{TestKit, TestActorRef, ImplicitSender}
import org.scalatest.{WordSpecLike, BeforeAndAfterAll}
import org.scalatest.matchers.MustMatchers

class ConnectionTest extends TestKit(ActorSystem("ConnectionSpec"))
  with WordSpecLike
  with MustMatchers 
  with BeforeAndAfterAll {

  override def afterAll() { system.shutdown() }

  "Server" must {
    "bind to port " in {
      // create server
      val server  = system.actorOf(Props[Server], name = "server")

      expectMsg("Bound to /127.0.0.1:8888")
    }    
  }
}

[build.sbt]

name := "MyApp"

version := "0.2"

scalaVersion := "2.10.4"

mainClass := Some("akka.Main")

resolvers += "Typesafe Repository" at "http://repo.typesafe.com/typesafe/releases/"

libraryDependencies +=
"com.typesafe.akka" %% "akka-actor" % "2.3.2"

libraryDependencies += 
"com.typesafe.akka" %% "akka-testkit" % "2.1.4" % "test"

libraryDependencies += 
"org.scalatest" % "scalatest_2.10" % "2.0" % "test"

You need to use the same version of Akka for testkit.

libraryDependencies += 
"com.typesafe.akka" %% "akka-testkit" % "2.1.4" % "test"

should be

libraryDependencies += 
"com.typesafe.akka" %% "akka-testkit" % "2.3.2" % "test"