Seaquel
SQL Server error code

SQL Server error 6201

SQL Server raises error 6201 at severity 16, which marks a problem with the query or data that you can correct.

Method "%ls" of type "%ls" in assembly "%.*ls" is not marked as a mutator. Only mutators can be used to update the value of a CLR type.
Msg6201
Severity16
Group6000–6999

Source: Database Engine events and errors