Seaquel
SQL Server error code

SQL Server error 1426

SQL Server raises error 1426 at severity 16, which marks a problem with the query or data that you can correct.

To issue ALTER DATABASE SET WITNESS, all three server instances must be interconnected, and the mirror database must be caught up. When these conditions are met, reissue the command.
Msg1426
Severity16
Group1000–1999

Source: Database Engine events and errors