Seaquel
SQL Server error code

SQL Server error 2521

SQL Server raises error 2521 at severity 16, which marks a problem with the query or data that you can correct.

Could not find database ID %d. The database ID either does not exist, or the database was dropped before a statement tried to use it. Verify if the database ID exists by querying the sys.databases catalog view.
Msg2521
Severity16
Group2000–2999

Source: Database Engine events and errors