Seaquel
SQL Server error code

SQL Server error 2550

SQL Server raises error 2550 at severity 16, which marks a problem with the query or data that you can correct.

The index "%.*ls" (partition %ld) on table "%.*ls" cannot be reorganized because it is being reorganized by another process.
Msg2550
Severity16
Group2000–2999

Source: Database Engine events and errors