Oracle Error Message
RMAN-05521: DUPLICATE without CATALOG and TARGET not open requires that UNDO TABLESPACE is specified
Reason for the Error
A DUPLICATE was attempted when target database was not open without connection to a recovery catalog. It is necessary that the list of tablespaces with undo segments is provided with the UNDO TABLESPACE clause.
Solution
Retry the command specifying the list of tablespaces with undo segments using the UNDO TABLESPACE clause.