Error when excuting mapreduce

hello to all

i am writing a mapreduce program, but i want to execute it it gives this error


Jul 19, 2010 5:06:31 PM org.apache.hadoop.mapred.JobClient monitorAndPrintJob
INFO: Task Id : attempt_201007191410_0002_m_000000_0, Status : FAILED
java.lang.NullPointerException
    at org.apache.hadoop.io.serializer.SerializationFactory.getSerializer(SerializationFactory.java:73)
    at org.apache.hadoop.mapred.MapTask$MapOutputBuffer.<init>(MapTask.java:797)
    at org.apache.hadoop.mapred.MapTask.runOldMapper(MapTask.java:350)
    at org.apache.hadoop.mapred.MapTask.run(MapTask.java:307)
    at org.apache.hadoop.mapred.Child.main(Child.java:170)

please can any one help me?

regards