Oracle Message RMAN-05026 - WARNING: presuming following set of tablespaces applies to specified point in time

ERRORWARNING: presuming following set of tablespaces applies to specified point in time
CAUSERMAN assumes that the current set of tablespaces with undo segments is the same set that was in use at the specified Point-in-Time. If the set of tablespaces with undo segments changes, the recovery fails. If recovery fails, use the optional UNDO TABLESPACE clause of the RECOVER command to specify the correct set of tablespaces.
ACTIONRMAN assumes that the current set of tablespaces with undo segments is the same set that was in use at the specified Point-in-Time. If the set of tablespaces with undo segments changes, the recovery fails. If recovery fails, use the optional UNDO TABLESPACE clause of the RECOVER command to specify the correct set of tablespaces.