This error can be caused when you drop tablespaces from a database in 11.2.0 – Bug 9909828. I also saw this happen after rebuilding a Data Guard Standby (11.2.0) after it failed with an ORA 600 error and wouldn’t work. As I’ve found this solution actually fixes quite a few RMAN issues.
You can correct this (and other things) by unregistering the database from the catalog and then registering again.
rman connect target connect catalog rcatmgr@p10dba <password> unregister database; .... register database; <run your backup again. exit