Seaquel
SQL Server error code

SQL Server error 256

SQL Server raises error 256 at severity 16, which marks a problem with the query or data that you can correct.

The data type %ls is invalid for the %ls function. Allowed types are: char/varchar, nchar/nvarchar, and binary/varbinary.
Msg256
Severity16
Group0–999

Source: Database Engine events and errors