我正在学习kafka，现在我遇到了一些我在这里找到的示例代码的问题：https://cwiki.apache.org/confluence/display/KAFKA/Consumer+Group+Example
每次运行代码时都会引发异常：
Exception in thread "main" kafka.common.ConsumerRebalanceFailedException: ttt_NB644-1475151991986-76dfa03f can't rebalance after 4 retries
at kafka.consumer.ZookeeperConsumerConnector$ZKRebalancerListener.syncedRebalance(ZookeeperConsumerConnector.scala:670)
at kafka.consumer.ZookeeperConsumerConnector.kafka$consumer$ZookeeperConsumerConnector$$reinitializeConsumer(ZookeeperConsumerConnector.scala:977)
at kafka.consumer.ZookeeperConsumerConnector.consume(ZookeeperConsumerConnector.scala:264)
at kafka.javaapi.consumer.ZookeeperConsumerConnector.createMessageStreams(ZookeeperConsumerConnector.scala:85)
at kafka.javaapi.consumer.ZookeeperConsumerConnector.createMessageStreams(ZookeeperConsumerConnector.scala:97)
at com.glowbyte.kafka.consumertest.ConsumerGroupExample.run(ConsumerGroupExample.java:44)
at com.glowbyte.kafka.consumertest.ConsumerGroupExample.main(ConsumerGroupExample.java:78)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:140)
我使用的kafka版本是0.10，最新版本。 只有一个主题有一个代理和两个分区，我正在尝试用2个线程运行代码。
与此同时，另一个代码，更简单，在同一环境中成功运行，同时还有2个线程。所以我想了解造成描述异常的原因。感谢。