ORA-19915: unable to encrypt pre-10.2 files
Cause: An RMAN encrypted backup was requested, but this backup includes one or more archived logs that were generated by an older release of Oracle. These archived logs cannot be encrypted
Action: Back up the older logs without encryption. Logs created with Oracle release 10.2 and greater can be encrypted
https://support.oracle.com/
http://www.oracle.com/