ORA-16434: archive log for branch string thread string sequence string cannot be queued
Cause:
An archive log needed by the standby database to resolve a redo gap was not found on the source database. This is a fatal situation during a switchover or far sync instance assisted failover because the source database waits for the target standby to be clear of all archive log gaps before allowing the operation to proceed. If a redo gap cannot be resolved during these operations, the operation cannot succeed so it must be failed.
Action:
If the specified log is listed in V$ARCHIVED_LOG for the DEST_ID of the local destination on the source database but no longer exists at that location on disk, the archived log can be copied back to that location to allow gap processing to automatically resolve the gap. If the specified log has been purged from V$ARCHIVED_LOG, the archived log can be copied to disk on either the source or destination database and registered using the ALTER DATABASE REGISTER OR REPLACE LOGFILE command.