Seaquel
SQL Server error code

SQL Server error 1904

SQL Server raises error 1904 at severity 16, which marks a problem with the query or data that you can correct.

The %S_MSG '%.*ls' on table '%.*ls' has %d columns in the key list. The maximum limit for %S_MSG key column list is %d.
Msg1904
NameKEYCOUNT
Severity16
Group1000–1999

What it means

The key column list for the specified index or statistics exceeds the maximum number of columns allowed.

Source: Database Engine events and errors