NPE in FSNamesystem.addStoredBlock(...)

2008-07-21 22:30:43,489 INFO org.apache.hadoop.ipc.Server: IPC Server handler 9 on 59403,
  call blockReceived(DatanodeRegistration(DN_HOST:58052, storageID=DS-YYYYYY, infoPort=55243, ipcPort=50020), [Lorg.apache.hadoop.hdfs.protocol.Block;@11e
725, [Ljava.lang.String;@15e4ae5) from DN_HOST:49527: error: java.io.IOException: java.lang.NullPointerException
java.io.IOException: java.lang.NullPointerException
        at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.addStoredBlock(FSNamesystem.java:2800)
        at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.blockReceived(FSNamesystem.java:3138)
        at org.apache.hadoop.hdfs.server.namenode.NameNode.blockReceived(NameNode.java:637)
        at sun.reflect.GeneratedMethodAccessor7.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$Server.call(RPC.java:452)
        at org.apache.hadoop.ipc.Server$Handler.run(Server.java:888)