Cause: The DB_UNIQUE_NAME specified for the destination does not match the DB_UNIQUE_NAME at the destination.
Action: Make sure the DB_UNIQUE_NAME specified in the LOG_ARCHIVE_DEST_n parameter defined for the destination matches the DB_UNIQUE_NAME parameter defined at the destination.
The error message was misleading in my case; my bad was that the log_archive_config on primary and the standby did not agree (actually it was nothing on standby). This error may show up in alert-log (didn't every time with me), and will also show up in v$archive_dest:
If this is your case, check log_archive_config on all nodes.