我在我的asp.net 3.5 a3层应用程序中使用crystal report时出现以下错误

The type or namespace name ‘CrystalReportViewer’ does not exist in the namespace ‘CrystalDecisions.Web’ (are you missing an assembly reference?)

我包含的名称空间是：

@H_301_8@using System; using System.Collections; using System.Configuration; using System.Data; using System.Linq; using System.Web; using System.Web.Security; using System.Web.UI; using System.Web.UI.WebControls; using System.Web.UI.WebControls.WebParts; using System.Web.UI.HtmlControls; using System.Xml.Linq; using MorvelNew.Report; using System.Data.sql; using System.Data.sqlClient; using System.Data.sqlTypes; using CrystalDecisions.CrystalReports.Engine; using CrystalDecisions.Web;