Seaquel
SQL Server error code

SQL Server error 9728

SQL Server raises error 9728 at severity 16, which marks a problem with the query or data that you can correct.

Cannot find the security certificate because the lookup database principal ID (%i) is not valid. The security principal may have been dropped after the conversation was created.
Msg9728
Severity16
Group9000–9999

Source: Database Engine events and errors