无法删除外键约束

Question

表格定义：

CREATE TABLE [dbo].[Visualization_ComponentLayouts]
(
    [ComponentLayoutId] [int] IDENTITY(1,1) NOT NULL,
    [ComponentId] [int] NOT NULL,
    [LayoutId] [int] NOT NULL,
    [UnitTypeId] [int] NOT NULL,
    [ProjectId] [int] NOT NULL,
    [CreatedBy] [int] NULL,
    [ModifiedBy] [int] NULL,
 CONSTRAINT [PK_Visualization_ComponentLayouts] PRIMARY KEY CLUSTERED 
(
    [ComponentLayoutId] 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

ALTER TABLE [dbo].[Visualization_ComponentLayouts] WITH NOCHECK 
   ADD CONSTRAINT [FK_Visualization_ComponentLayouts_Visualization_ComponentInfo] 
   FOREIGN KEY([ComponentId])
   REFERENCES [dbo].[Visualization_ComponentInfo] ([ComponentId])
GO

ALTER TABLE [dbo].[Visualization_ComponentLayouts] CHECK CONSTRAINT [FK_Visualization_ComponentLayouts_Visualization_ComponentInfo]
GO

ALTER TABLE [dbo].[Visualization_ComponentLayouts] WITH CHECK 
   ADD CONSTRAINT [FK_Visualization_ComponentLayouts_Visualization_Layouts] 
   FOREIGN KEY([LayoutId], [ProjectId])
   REFERENCES [dbo].[Visualization_Layouts] ([LayoutId], [ProjectId])
GO

ALTER TABLE [dbo].[Visualization_ComponentLayouts] CHECK CONSTRAINT [FK_Visualization_ComponentLayouts_Visualization_Layouts]
GO

查询放弃约束：

ALTER TABLE Visualization_ComponentLayouts
DROP CONSTRAINT FK_Visualization_ComponentLayouts_Visualization_Layouts

执行上面的drop查询时出错：

  

'FK_Visualization_ComponentLayouts_Visualization_Layouts'不是   约束。无法删除约束。查看以前的错误。

在SQL Server Management Studio中，在对象资源管理器中，当我展开表节点时，当我展开约束节点时，在那里没有列出任何约束。

执行查询时：EXEC sp_help 'Visualization_ComponentLayouts' 我得到了以下信息：

我做错了什么？