The Identity property can't be set on column <Columnname> because it allows null values. (Visual Database Tools)

Identity columns contain system-generated sequential values that uniquely identify each row within the table. Therefore, identity columns cannot have null values.

For more information, see How to: Modify Column Identity Properties (Visual Database Tools) and How to: Modify Null Options on Columns (Visual Database Tools).

See Also

Concepts

Error Messages in Visual Database Tools

Help and Information

Getting SQL Server 2005 Assistance