Have you ever seen this exception?
2013/03/25 12:08:32.020 WARN [ZookeeperConsumerConnector] [] 0_lu-ml-test10.bj-1364184411339-7c88f710 exception during commitOffsets java.lang.NullPointerException at org.I0Itec.zkclient.ZkConnection.writeData(ZkConnection.java:111) at org.I0Itec.zkclient.ZkClient$10.call(ZkClient.java:813) at org.I0Itec.zkclient.ZkClient.retryUntilConnected(ZkClient.java:675) at org.I0Itec.zkclient.ZkClient.writeData(ZkClient.java:809) at org.I0Itec.zkclient.ZkClient.writeData(ZkClient.java:777) at kafka.utils.ZkUtils$.updatePersistentPath(ZkUtils.scala:103) at kafka.consumer.ZookeeperConsumerConnector$$anonfun$commitOffsets$2$$anonfun$apply$4.apply(ZookeeperConsumerConnector.scala:251) at kafka.consumer.ZookeeperConsumerConnector$$anonfun$commitOffsets$2$$anonfun$apply$4.apply(ZookeeperConsumerConnector.scala:248) at scala.collection.Iterator$class.foreach(Iterator.scala:631) at scala.collection.JavaConversions$JIteratorWrapper.foreach(JavaConversions.scala:549) at scala.collection.IterableLike$class.foreach(IterableLike.scala:79) at scala.collection.JavaConversions$JCollectionWrapper.foreach(JavaConversions.scala:570) at kafka.consumer.ZookeeperConsumerConnector$$anonfun$commitOffsets$2.apply(ZookeeperConsumerConnector.scala:248) at kafka.consumer.ZookeeperConsumerConnector$$anonfun$commitOffsets$2.apply(ZookeeperConsumerConnector.scala:246) at scala.collection.Iterator$class.foreach(Iterator.scala:631) at kafka.utils.Pool$$anon$1.foreach(Pool.scala:53) at scala.collection.IterableLike$class.foreach(IterableLike.scala:79) at kafka.utils.Pool.foreach(Pool.scala:24) at kafka.consumer.ZookeeperConsumerConnector.commitOffsets(ZookeeperConsumerConnector.scala:246) at kafka.consumer.ZookeeperConsumerConnector.autoCommit(ZookeeperConsumerConnector.scala:232) at kafka.consumer.ZookeeperConsumerConnector$$anonfun$1.apply$mcV$sp(ZookeeperConsumerConnector.scala:126) at kafka.utils.Utils$$anon$2.run(Utils.scala:58) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471) at java.util.concurrent.FutureTask$Sync.innerRunAndReset(FutureTask.java:351) at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:178) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:178) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603) at java.lang.Thread.run(Thread.java:722)