一个RemoteException，不知道怎么解决

一个RemoteException，不知道如何解决？
升级到weblogic 10后，运行一段时间后，突然出现以下exception，一直没有恢复好。
不知道什么原因？应该怎么解决呢？

Caused by: java.rmi.RemoteException: EJB Exception: ; nested exception is:
  java.lang.NullPointerException
  at weblogic.rjvm.ResponseImpl.unmarshalReturn(ResponseImpl.java:217)
  at weblogic.rmi.cluster.ClusterableRemoteRef.invoke(ClusterableRemoteRef.java:338)
  at weblogic.rmi.cluster.ClusterableRemoteRef.invoke(ClusterableRemoteRef.java:252)
  at com.psa.infra.communityrealm.ejb.UserInfoServiceBean_7mbutc_EOImpl_1000_WLStub.getClientUserInfo(Unknown Source)
  at com.psa.infra.communityrealm.client.UserInfoServices.getClientUserInfo(UserInfoServices.java:148)
  ... 27 more
Caused by: java.lang.NullPointerException
  at org.apache.log4j.WriterAppender.subAppend(WriterAppender.java:301)
  at com.psa.common.logging.DatedFileAppender.append(DatedFileAppender.java:245)
  at org.apache.log4j.AppenderSkeleton.doAppend(AppenderSkeleton.java:230)
  at org.apache.log4j.helpers.AppenderAttachableImpl.appendLoopOnAppenders(AppenderAttachableImpl.java:65)
  at org.apache.log4j.Category.callAppenders(Category.java:203)
  at org.apache.log4j.Category.forcedLog(Category.java:388)
  at org.apache.log4j.Category.debug(Category.java:257)
  at com.portnet.security.util.SimpleLogger.debug(SimpleLogger.java:95)
  at com.psa.infra.communityrealm.ejb.UserInfoServiceBeanImpl.getClientUserInfo(UserInfoServiceBeanImpl.java:40)
  at com.psa.infra.communityrealm.ejb.UserInfoServiceBean_7mbutc_EOImpl.getClientUserInfo(UserInfoServiceBean_7mbutc_EOImpl.java:428)
  at com.psa.infra.communityrealm.ejb.UserInfoServiceBean_7mbutc_EOImpl_WLSkel.invoke(Unknown Source)
  at weblogic.rmi.internal.BasicServerRef.invoke(BasicServerRef.java:589)
  at weblogic.rmi.cluster.ClusterableServerRef.invoke(ClusterableServerRef.java:224)
  at weblogic.rmi.internal.BasicServerRef$1.run(BasicServerRef.java:479)
  at weblogic.security.acl.internal.AuthenticatedSubject.doAs(AuthenticatedSubject.java:363)
  at weblogic.security.service.SecurityManager.runAs(Unknown Source)
  at weblogic.rmi.internal.BasicServerRef.handleRequest(BasicServerRef.java:475)
  at weblogic.rmi.internal.BasicServerRef.access$300(BasicServerRef.java:59)
  at weblogic.rmi.internal.BasicServerRef$BasicExecuteRequest.run(BasicServerRef.java:1016)
  at weblogic.work.ExecuteThread.execute(ExecuteThread.java:200)
  at weblogic.work.ExecuteThread.run(ExecuteThread.java:172)

------解决方案--------------------
com.psa.infra.communityrealm.ejb.UserInfoServiceBean_7mbutc_EOImpl_1000_WLStub.getClientUserInfo(Unknown Source) 
at com.psa.infra.communityrealm.client.UserInfoServices.getClientUserInfo(UserInfoServices.java:148) 
... 27 more 
Caused by: java.lang.NullPointerException 
-------------------------------------------
NullPointerException，检查使用的对象为何为NULL