方式来引用 DLL 是：

1. 在Solution Explorer中，选择项目。


2. 在项目菜单，单击添加引用。
      打开添加引用对话框。


3. 选择表示要引用组件类型的标签。
      （如果您没有在列表中找到您的.dll，然后去浏览选项卡，找到它在你的目录）

在 MSDN的文章 ，包括已安装的库。

这是有另一种方式来做到这一点。

 Error 3 The type or namespace name 'AjaxControlToolkit' could not be found
 in the global namespace (are you missing an assembly reference?)   
 D:\My App\table\PopUpdata.aspx.designer.cs 58 27 table.

I have Declared this javascript but what is the problem.

<%@ Page Title="Show Data From Menu" Language="C#" MasterPageFile="~/Site.Master" AutoEventWireup="true" CodeBehind="PopUpdata.aspx.cs" Inherits="table.PopUpdata" %>

<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="asp" %>

Way to reference a dll is:

1. In Solution Explorer, select the project.
2. On the Project menu, click Add Reference. The Add Reference dialog box opens.
3. Select the tab indicating the type of component you want to reference. (If you don't find your .dll in the list, then go to the browse tab and find it in your directory)

An article on MSDN to include installed libraries.

an There is another way to do it.