ORA-16548: database not enabled

PROBLEM

The standby DB is/stays disabled (cannot be enabled)

DGMGRL> show configuration;

Configuration - MYDB

  Protection Mode: MaxAvailability

  Databases:

    MYDB_PRIMARY - Primary database

    MYDB_STANDBY - Physical standby database (disabled)

Fast-Start Failover: DISABLED

OR

DGMGRL> edit database MYDB_STANDBY . . .

Error: ORA-16548: database not enabled

and the . . .

DGMGRL> enable database MYDB_STANDBY;

Enabled.

. . . does not work. Despite showing "Enabled." the DB is not really enabled.

The DataGuard Log file drc<SID>.log(cd /u00/app/oracle/diag/rdbms/mydb_primary/mydb/trace
or - withTrivadis Baseenv:  cdd; cd trace) 

shows:

. . .

ENABLE DATABASE MYDB_STANDBY

Warning, database MYDB_STANDBY that was marked for re-creation

      will be re-enabled. There may be errors or warnings

      if the database was not properly re-created. See this

      log and the alert log for more details.

Metadata Resync failed. Status = ORA-16603

. . .

POSSIBLE CAUSE

I caused the problem myself, because I've tried to solve a Data Guard problem by re-creating the configuration using a configuration name in upper case letters instead of re-using the same name as before (with lower case letters).

POSSIBLE SOLUTION

On the STANDBY DB

DGMGRL> connect sys/<Pwd>@MYDB_PRIMARY

Connected.

DGMGRL> remove configuration;

Error: ORA-16627: operation disallowed since no standby databases would remain to support protection mode

Failed.

DGMGRL> disable configuration;

Disabled.

DGMGRL> remove configuration;

Removed configuration

On the PRIMARY DB

DGMGRL> connect sys/<Pwd>@MYDB_PRIMARY

DGMGRL> enable database MYDB_STANDBY;

Enabled.