I got this error on DGMGRL command line when I was configuring 11g Dataguard and I issued

DGMGRL> show configuration;

This error was coming as my standby database was started using pfile,

I shutdown the standby database and restarted it using spfile and the problem was resolved.

Another time I got this error was when I changed the IP address of the machine after dataguard had been configured. I deleted the tnsnames.ora and listener.ora entries and recreated them. Then it started working.

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