Problem signalling task 32039 with KILL; exit = 6

At times I see some of the tasks being failed due to OutOfMemoryError with a stack trace in syslogs as-

2012-02-13 08:09:42,003 FATAL org.apache.hadoop.mapred.Child: Error running child : java.lang.OutOfMemoryError: unable to create new native thread at java.lang.Thread.start0(Native Method) at java.lang.Thread.start(Thread.java:640) at com.mapr.fs.MapRFsInStream.getCacheSize(MapRFsInStream.java:64) at com.mapr.fs.Inode.<init>(Inode.java:112) at com.mapr.fs.MapRFsInStream.<init>(MapRFsInStream.java:36) at com.mapr.fs.MapRClient.open(MapRClient.java:191) at com.mapr.fs.MapRFileSystem.open(MapRFileSystem.java:307) at org.apache.hadoop.fs.FileSystem.open(FileSystem.java:460) at org.apache.hadoop.mapred.Merger$Segment.init(Merger.java:204) at org.apache.hadoop.mapred.Merger$Segment.access$100(Merger.java:165) at org.apache.hadoop.mapred.Merger$MergeQueue.merge(Merger.java:444) at org.apache.hadoop.mapred.Merger$MergeQueue.merge(Merger.java:407) at org.apache.hadoop.mapred.Merger.merge(Merger.java:77) at org.apache.hadoop.mapred.MapTask$MapOutputBuffer.mergePerPartition(MapTask.java:1885) at org.apache.hadoop.mapred.MapTask$MapOutputBuffer.flush(MapTask.java:1312) at org.apache.hadoop.mapred.MapTask$NewOutputCollector.close(MapTask.java:589) at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:656) at org.apache.hadoop.mapred.MapTask.run(MapTask.java:325) at org.apache.hadoop.mapred.Child$4.run(Child.java:270) at java.security.AccessController.doPrivileged(Native Method) at javax.security.auth.Subject.doAs(Subject.java:396) at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1109) at org.apache.hadoop.mapred.Child.main(Child.java:264)

I would expect such tasks to be killed and retried. Strangely sometimes such tasks are not killed and stderr logs will have something like-

Exception in thread "main" org.apache.hadoop.ipc.RemoteException: java.io.IOException: Problem signalling task 32039 with KILL; exit = 6 at org.apache.hadoop.mapred.LinuxTaskController.signalTask(LinuxTaskController.java:339) at org.apache.hadoop.mapred.JvmManager$JvmManagerForType$JvmRunner.kill(JvmManager.java:704) at org.apache.hadoop.mapred.JvmManager$JvmManagerForType.killJvmRunner(JvmManager.java:351) at org.apache.hadoop.mapred.JvmManager$JvmManagerForType.killJvm(JvmManager.java:330) at org.apache.hadoop.mapred.JvmManager$JvmManagerForType.taskKilled(JvmManager.java:321) at org.apache.hadoop.mapred.JvmManager.taskKilled(JvmManager.java:170) at org.apache.hadoop.mapred.TaskRunner.kill(TaskRunner.java:810) at org.apache.hadoop.mapred.TaskTracker$TaskInProgress.kill(TaskTracker.java:4474) at org.apache.hadoop.mapred.TaskTracker$TaskInProgress.jobHasFinished(TaskTracker.java:4446) at org.apache.hadoop.mapred.TaskTracker.purgeTask(TaskTracker.java:3353) at org.apache.hadoop.mapred.TaskTracker.fatalError(TaskTracker.java:4878) at sun.reflect.GeneratedMethodAccessor21.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:964) at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1318) at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1314) at java.security.AccessController.doPrivileged(Native Method) at javax.security.auth.Subject.doAs(Subject.java:396) at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1109) at org.apache.hadoop.ipc.Server$Handler.run(Server.java:1312) at org.apache.hadoop.ipc.Client.call(Client.java:1071) at org.apache.hadoop.ipc.RPC$Invoker.invoke(RPC.java:275) at $Proxy0.fatalError(Unknown Source) at org.apache.hadoop.mapred.Child.main(Child.java:324)

What could be wrong here?