an error occurs which status code is 800

Dear Symantec Team

an error occured today when i check the status of NBU's Backup which version is 7.0 running on Windows Server 2008.

Please Kindly help me to sovle the issue,here is the error information as below:

2013/3/31 11:00:36 - Requsting resource SIH_SPDB
2013/3/31 11:00:36 - Requsting resource sih-netbackup.NBU_CLIENT.MAXJOBS.SIH-SQLSPDB
2013/3/31 11:00:36 - Requsting resource sih-netbackup.NBU_POLICY.MAXJOBS.SIH_SPDB_SQL_DIFF
2013/3/31 11:00:36 - error nbjm(PID=6988) NBU status: 800, EMM status: Disk volume is down   
Requsting resource failed(800)