ORA-19914: unable to encrypt backup

admin

ORA-19914: unable toencrypt backup
Cause: RMANcould not create an encrypted backup. This message will be
accompanied by other messages that give more details about why the encrypted
backup could not be created. The most common reason for this message is that
you are trying to create a backup that can be transparently decrypted, and the
database external security device is not open.
Action: Ifthe external security device is not open, then open it. If the external
security device is not configured, then the only type of encrypted backup thatyou
can create is a password-based backup.