When you are using the RMAN duplicate method, RMAN would be throwing out the below error at the time of duplication if the target database you are using has the block change tracking enabled.
ORA-19755 ORA-19750 ORA-27037 with the OS error specifying the unavailability of the BCT file.
To overcome this error, you need to disable the change tracking on the source (target) database.
I've tested a couple of scenarios with BCT being enabled on the target database and trying to perform the cloning using the "Active database" technique but I could not replicate the issue what you are facing. I am not sure why you are facing this error when you are performing the duplication using "Active database".
When ever you tar untar oracle_home to distant location, remove souce BCT file that gets copied in target before u start active database. SO while cloning this source bct file if exists then it will nt create bct again, so alwayd put bct off or delete it form target /dbs location