Error 830 "All compatible drive paths are down, but media is available" but in the console everything is green

Hello,

Last weekend, the backups failed with the status 830 and the error, All compatible drive paths are down, but media is available

While, in the NBU console, everything was green

Here is a log of the job:

08/09/2013 00:20:00 - requesting resource srvseaco-nbu-1-hcart-robot-tld-0
08/09/2013 00:20:00 - requesting resource srvseaco-nbu-1.NBU_CLIENT.MAXJOBS.srvseaco-ctx1.seaco.intranet
08/09/2013 00:20:00 - requesting resource srvseaco-nbu-1.NBU_POLICY.MAXJOBS.CTX1
08/09/2013 00:20:00 - Error nbjm(pid=588) NBU status: 830, EMM status: All compatible drive paths are down, but media is available
drive(s) unavailable or down(830)

How can i diagnose this issue please? and is there anything to do to prevent this from happening again?

Regards!