The primary key or UNIQUE constraint cannot be changed until its existing relationships are deleted. (Visual Database Tools)

You cannot change a table's primary key or unique constraint while other foreign key relationships are still in place. To change a table's primary key or unique constraint, first delete all existing relationships for the table.

For more information, see How to: Delete Relationships (Visual Database Tools).

See Also

Concepts

Error Messages in Visual Database Tools

Help and Information

Getting SQL Server 2005 Assistance