Error writing to highwatermark file

[wan...@act.buaa.edu.cn]

Hi,
I use 2 brokers as a cluster, and write data into nfs.

I encountered this problem several days after starting the brokers :
FATAL [Replica Manager on Broker 1]: Error writing to highwatermark file:  
(kafka.server.ReplicaManager)
 java.io.IOException: File rename from 
/nfs/trust-machine/machine11/kafka-logs/replication-offset-checkpoint.tmp to 
/nfs/trust-machine/machine11/kafka-logs/replication-offset-checkpoint failed.

why?
My kafka version is 0.8.1.

Thanks!