"unknown standby database destination"
*Cause: A standby database destination was specified that was not accessed
by another instance. If the initialization parameter
LOG_ARCHIVE_CONFIG does not define a DG_CONFIG, this mismatch
may be due to a standby database having been restarted recently.
*Action: Ensure that at each instance the set of standby databases referred
to by LOG_ARCHIVE_DEST_n initialization parameters is the same
and define a DG_CONFIG at each instance to identify those databases