将表添加到LINQ to SQL数据上下文

我正试图将数据库中的一个表添加到LINQ to SQL数据上下文中。它不允许我这样做。看着visual studio中设计师的桌子，它似乎没有意识到Id是主键。我看不出这张桌子有什么毛病。任何想法都将不胜感激。

这是我的桌子；

USE [fldt_bt_wbc]
GO
SET ANSI_NULLS ON
GO        
SET QUOTED_IDENTIFIER ON
GO        
SET ANSI_PADDING ON
GO        
CREATE TABLE [dbo].[btRequests](
    [ID] [int] IDENTITY(1,1) NOT NULL,
    [UserID] [varchar](25) NOT NULL,
    [RequestType] [int] NOT NULL,
    [DateTime] [datetime] NOT NULL,
    [Status] [varchar](20) NULL,
    [ConversationID] [varchar](50) NULL,
CONSTRAINT [PK_btRequests] PRIMARY KEY CLUSTERED 
(
    [ID] 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 ANSI_PADDING OFF
GO
ALTER TABLE [dbo].[btRequests]  WITH CHECK ADD  CONSTRAINT [FK_btRequests_RequestType] FOREIGN KEY([RequestType])
REFERENCES [dbo].[RequestType] ([ID])
GO
ALTER TABLE [dbo].[btRequests] CHECK CONSTRAINT [FK_btRequests_RequestType]
GO