OK the sysdba is the SUPERDBA but the login on db level did not work (-4008: Unknown user name / password)
I suggest to do the following:
1)Reset the the sysdba password in the database with
dbmcli -d SDB -u DBM,control db_execute alter password SUPERDBA ADMIN
2)Then test the connection with sqlcli to check the password in the database.
sqlcli –d SDB –u superdba,admin select sysdba from sysdd.version
3) Now try to load the system tables
dbmcli -d SDB -u DBM,control load_systab -u SUPERDBA,ADMIN