Error Code: ORA-16664: unable to receive the result from a database
Case: You can see the redo shipping is working fine from Primary to standby DB. you can notice this error when you try to enable the DG broker.
Test the following:
1. connection to standby from Primary server - should be good if the redo shipping is fine
2. connection from standby to Primary server
This could be the cause - As during normal redo shipping we don't need the vice versa connection from standby to Primary but when you enable the DG Broker it needs that for the auto switchover, fail over.
Some other causes for the same issue:
The logon trigger was preventing the connection from the standby database during a switchover.
Fix: disable the logon trigger in primary database. (Metalink id 1530881.1)
Check the non default port used in connect string of both primary and standby(tnsnames.ora). Metalink id 1228797.1
