RMAN-05537: DUPLICATE without TARGET connection when auxiliary instance is started

Problem:

Error while creating auxiliary database from target

RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of Duplicate Db command at 05/06/2019 13:25:01
RMAN-05501: aborting duplication of target database
RMAN-05537: DUPLICATE without TARGET connection when auxiliary instance is started with spfile cannot use SPFILE clause

Solution: 

remove spfile or create pfile from spfile and start database using pfile.

create pfile from spfile

rm spfile.ora

startup nomount;