Seaquel
SQL Server error code

SQL Server error 6373

SQL Server raises error 6373 at severity 16, which marks a problem with the query or data that you can correct.

The expression specified for path '%.*ls' is not allowed for selective XML index '%.*ls'. It is only allowed to index simple path expressions without predicates.
Msg6373
Severity16
Group6000–6999

Source: Database Engine events and errors