我正在尝试在Hadoop中运行wordcount作业。由于先前的错误，我不得不关闭NameNode的安全模式。但是，现在，在尝试运行作业时，我收到以下错误：
14/08/06 14:49:08 INFO mapreduce.Job: map 1% reduce 0%
14/08/06 14:49:25 INFO mapreduce.Job: Task Id : attempt_1407336345567_0002_m_000158_0, Status : FAILED
Error: org.apache.hadoop.hdfs.BlockMissingException: Could not obtain block: BP-971868671-192.168.50.2-1406571670535:blk_1073743276_2475 file=/wikidumps/enwiki-20130904-pages-meta-history3.xml-p000032706p000037161
at org.apache.hadoop.hdfs.DFSInputStream.chooseDataNode(DFSInputStream.java:838)
at org.apache.hadoop.hdfs.DFSInputStream.blockSeekTo(DFSInputStream.java:526)
at org.apache.hadoop.hdfs.DFSInputStream.readWithStrategy(DFSInputStream.java:749)
at org.apache.hadoop.hdfs.DFSInputStream.read(DFSInputStream.java:793)
at java.io.DataInputStream.read(DataInputStream.java:100)
at org.apache.hadoop.util.LineReader.readDefaultLine(LineReader.java:211)
at org.apache.hadoop.util.LineReader.readLine(LineReader.java:174)
at org.apache.hadoop.mapreduce.lib.input.LineRecordReader.nextKeyValue(LineRecordReader.java:164)
at org.apache.hadoop.mapred.MapTask$NewTrackingRecordReader.nextKeyValue(MapTask.java:532)
at org.apache.hadoop.mapreduce.task.MapContextImpl.nextKeyValue(MapContextImpl.java:80)
at org.apache.hadoop.mapreduce.lib.map.WrappedMapper$Context.nextKeyValue(WrappedMapper.java:91)
at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:144)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:763)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:339)
at org.apache.hadoop.mapred.YarnChild$2.run(YarnChild.java:162)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:415)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1491)
at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:157)
日志文件未显示任何特定错误。有谁知道这个错误的原因？提前谢谢！