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SQL Server error code

SQL Server error 3994

SQL Server raises error 3994 at severity 16, which marks a problem with the query or data that you can correct.

User defined routine, trigger or aggregate tried to rollback a transaction that is not started in that CLR level. An exception will be thrown to prevent execution of rest of the user defined routine, trigger or aggregate.
Msg3994
Severity16
Group3000–3999

Source: Database Engine events and errors