Seaquel
SQL Server error code

SQL Server error 5064

SQL Server raises error 5064 at severity 16, which marks a problem with the query or data that you can correct.

Changes to the state or options of database '%.*ls' cannot be made at this time. The database is in single-user mode, and a user is currently connected to it.
Msg5064
Severity16
Group5000–5999

Source: Database Engine events and errors