ArrayStoreException on mapping RDD on cluster

import org.apache.spark.{SparkConf, SparkContext, Partitioner}
import org.apache.spark.SparkContext._

object twitterAggregation extends App {

  val conf = new SparkConf()
      .setMaster("spark://ec2-x-x-x-x.compute-1.amazonaws.com:7077")
      //.setMaster("local")
      .setAppName("foo")
      .setJars(List("target/scala-2.10/foo_2.10-0.0.1.jar"))
      .setSparkHome("/root/spark/")
  val sc = new SparkContext(conf)
  sc.parallelize(Seq("b")).map(identity).collect
}

14/02/28 18:41:10 WARN scheduler.TaskSetManager: Lost TID 1 (task 0.0:1)
14/02/28 18:41:10 INFO scheduler.DAGScheduler: Completed ResultTask(0, 0)
14/02/28 18:41:10 WARN scheduler.TaskSetManager: Loss was due to java.lang.ArrayStoreException
java.lang.ArrayStoreException: [Ljava.lang.String;
	at scala.runtime.ScalaRunTime$.array_update(ScalaRunTime.scala:88)
	at scala.Array$.slowcopy(Array.scala:81)
	at scala.Array$.copy(Array.scala:107)
	at scala.collection.mutable.ResizableArray$class.copyToArray(ResizableArray.scala:77)
	at scala.collection.mutable.ArrayBuffer.copyToArray(ArrayBuffer.scala:47)
	at scala.collection.TraversableOnce$class.copyToArray(TraversableOnce.scala:241)
	at scala.collection.AbstractTraversable.copyToArray(Traversable.scala:105)
	at scala.collection.TraversableOnce$class.toArray(TraversableOnce.scala:249)
	at scala.collection.AbstractTraversable.toArray(Traversable.scala:105)
	at scala.collection.TraversableOnce$class.toArray(TraversableOnce.scala:252)
	at scala.collection.AbstractIterator.toArray(Iterator.scala:1157)
	at org.apache.spark.rdd.RDD$$anonfun$4.apply(RDD.scala:602)
	at org.apache.spark.rdd.RDD$$anonfun$4.apply(RDD.scala:602)
	at org.apache.spark.SparkContext$$anonfun$runJob$4.apply(SparkContext.scala:884)
	at org.apache.spark.SparkContext$$anonfun$runJob$4.apply(SparkContext.scala:884)
	at org.apache.spark.scheduler.ResultTask.runTask(ResultTask.scala:109)
	at org.apache.spark.scheduler.Task.run(Task.scala:53)
	at org.apache.spark.executor.Executor$TaskRunner$$anonfun$run$1.apply$mcV$sp(Executor.scala:213)
	at org.apache.spark.deploy.SparkHadoopUtil.runAsUser(SparkHadoopUtil.scala:49)
	at org.apache.spark.executor.Executor$TaskRunner.run(Executor.scala:178)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at java.lang.Thread.run(Thread.java:744)