Oracle RMAN backup job failed with "ORA-00230: operation disallowed: snapshot control file enqueue unavailable"
There may also be various "waiting for snapshot control file enqueue" entries in the NetVault Backup log.
The failure may occur with Oracle Server (Rdbms) Versions below 11.2.
Oracle Bug 7450366 - "RMAN Autobackup fails with unable to obtain snapshot enqueue (ORA-230)".
See Oracle Article ID 7450366.8 for more information.
This problem is resolved in Oracle 126.96.36.199 (Base Release).
Alternately, work around the problem as outlined in Solution SOL80291 -
BakBone SFDC Solution Number: 00002363