Errors during starting MapReduce2

[xiong]

Hi, everyone,

During starting MapReduce2 (where the ambari version is from trunk) , the webUI 
display  as follow,

    

and the log of HistoryClientService is as follow:
2013-10-10 17:44:28,914 INFO  service.AbstractService 
(AbstractService.java:start(94)) - Service:HistoryClientService is started.

but the webUI displays

 

what's wrong?

thank you.