Spark job success but with ERROR CoarseGrainedExecutorBackend: Driver disassociated - hadoop

Question

My spark version is 1.6.2 and runs on yarn.
The log of drive container reports SUCCEEDED as follows:
16/11/17 17:25:56 INFO ApplicationMaster: Final app status: SUCCEEDED, exitCode: 0
16/11/17 17:25:56 INFO ApplicationMaster: Unregistering ApplicationMaster with SUCCEEDED
However, The log of one executor container records an ERROR:
16/11/17 17:25:56 WARN CoarseGrainedExecutorBackend: An unknown (xxx-xxx-xxx-xxx:xxxx) driver disconnected.
16/11/17 17:25:56 ERROR CoarseGrainedExecutorBackend: Driver xxx-xxx-xxx-xxx:xxxx disassociated! Shutting down.
I think the job is succeeded because the output results are as expected.
But I want to know why the error was thrown and whether the job was really succeeded.
I find more info from the log of yarn NodeManager:
WARN org.apache.hadoop.yarn.server.nodemanager.DefaultContainerExecutor: Exception from container-launch with container ID: container_xxxxxxxxx and exit code: 1
ExitCodeException exitCode=1:
at org.apache.hadoop.util.Shell.runCommand(Shell.java:545)
at org.apache.hadoop.util.Shell.run(Shell.java:456)
at org.apache.hadoop.util.Shell$ShellCommandExecutor.execute(Shell.java:722)
at org.apache.hadoop.yarn.server.nodemanager.DefaultContainerExecutor.launchContainer(DefaultContainerExecutor.java:212)
at org.apache.hadoop.yarn.server.nodemanager.containermanager.launcher.ContainerLaunch.call(ContainerLaunch.java:302)
at org.apache.hadoop.yarn.server.nodemanager.containermanager.launcher.ContainerLaunch.call(ContainerLaunch.java:82)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Someone encounter the same question?
Thanks.