Seaquel
SQL Server error code

SQL Server error 8661

SQL Server raises error 8661 at severity 16, which marks a problem with the query or data that you can correct.

Cannot create the clustered index "%.*ls" on view "%.*ls" because the index key includes columns that are not in the GROUP BY clause. Consider eliminating columns that are not in the GROUP BY clause from the index key.
Msg8661
Severity16
Group8000–8999

Source: Database Engine events and errors