Seaquel
SQL Server error code

SQL Server error 1912

SQL Server raises error 1912 at severity 16, which marks a problem with the query or data that you can correct.

Could not proceed with index DDL operation on %S_MSG '%.*ls' because it conflicts with another concurrent operation that is already in progress on the object. The concurrent operation could be an online index operation on the same object or another concurrent operation that moves index pages like DBCC SHRINKFILE.
Msg1912
Severity16
Group1000–1999

Source: Database Engine events and errors