From your post:
-- #3 Table ------------------------------------------------------------------#3 Table
/****** Object: Table [dbo].[Orders] ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[Orders](
[OrderID] [Int] IDENTITY(1,1) NOT NULL,
[CustomerID] [int] NOT NULL,
[OrderNumber] [nvarchar] (50) NULL,
[OrderDate] [datetime] NULL,
CONSTRAINT [PK_Item] PRIMARY KEY CLUSTERED -- <<< Look here, the constraint name is the same as the constraint on the table Item
(
[OrderID] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF,
ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
SET IDENTITY_INSERT [dbo].[Orders] ON
INSERT [dbo].[Orders] ([OrderID], [CustomerID], [OrderNumber], [Orderdate])
VALUES (1, 1, N'10001', '6/15/2011')
INSERT [dbo].[Orders] ([OrderID], [CustomerID], [OrderNumber], [Orderdate])
VALUES (2, 2, N'10002', '6/16/2011')
INSERT [dbo].[Orders] ([OrderID], [CustomerID], [OrderNumber], [Orderdate])
VALUES (3, 1, N'10003', '6/17/2011')
INSERT [dbo].[Orders] ([OrderID], [CustomerID], [OrderNumber], [Orderdate])
VALUES (4, 2, N'10004', '6/18/2011')
SET INDENTITY_INSERT [dbo].[Orders] OFF