Simpana Client Failed to Perform Backup Task, View the Task

Simpana client failed to perform backup task, view the task status, reported the following error: libary mediaagent drive pool media []: Mount path is offlline advice: please check if the mount path is online and accessible " What can cause this?

A) Client offline
B) Media Server Offline
C) The client can not resolve the media server host name
D) backup media failure