Namenode constantly using up 100% CPU

Trying to figure out the exact cause, but CPU load of the namenode is constantly 100% without any file exchanges.

.log file of the namenode showing the following exception about every 20 seconds.

2006-11-27 16:02:07,199 INFO org.apache.hadoop.ipc.Server: IPC Server handler 5 on 8020 call error: java.io.IOException: java.util.NoSuchElementException
java.io.IOException: java.util.NoSuchElementException
at java.util.TreeMap$PrivateEntryIterator.nextEntry(TreeMap.java:1029)
at java.util.TreeMap$KeyIterator.next(TreeMap.java:1058)
at java.util.AbstractCollection.toArray(AbstractCollection.java:176)
at org.apache.hadoop.dfs.DatanodeDescriptor.getBlocks(DatanodeDescriptor.java:96)
at org.apache.hadoop.dfs.FSNamesystem.processReport(FSNamesystem.java:1446)
at org.apache.hadoop.dfs.NameNode.blockReport(NameNode.java:506)
at sun.reflect.GeneratedMethodAccessor11.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:387)
at org.apache.hadoop.ipc.Server$Handler.run(Server.java:518)

On some of the datanodes, .log file is showing

2006-11-27 16:03:57,542 WARN org.apache.hadoop.dfs.DataNode: org.apache.hadoop.ipc.RemoteException: java.io.IOException: java.util.NoSuchElementException
at java.util.TreeMap$PrivateEntryIterator.nextEntry(TreeMap.java:1029)
at java.util.TreeMap$KeyIterator.next(TreeMap.java:1058)
at java.util.AbstractCollection.toArray(AbstractCollection.java:176)
at org.apache.hadoop.dfs.DatanodeDescriptor.getBlocks(DatanodeDescriptor.java:96)
at org.apache.hadoop.dfs.FSNamesystem.processReport(FSNamesystem.java:1446)
at org.apache.hadoop.dfs.NameNode.blockReport(NameNode.java:506)
at sun.reflect.GeneratedMethodAccessor11.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:387)
at org.apache.hadoop.ipc.Server$Handler.run(Server.java:518)

at org.apache.hadoop.ipc.Client$Connection.run(Client.java:248)