出现找不到文件或程序集名称“Microsoft.Web.UI.WebControls”，或找不到它的一个依赖项的错误提示。急啊

错误如下：“/Webs”应用程序中的服务器错误。
--------------------------------------------------------------------------------分析器错误 
说明: 在分析向此请求提供服务所需资源时出错。请检查下列特定分析错误详细信息并适当地修改源文件。 分析器错误信息: 找不到文件或程序集名称“Microsoft.Web.UI.WebControls”，或找不到它的一个依赖项。源错误: 
行 1：  <%@ Register TagPrefix="iewc" Namespace="Microsoft.Web.UI.WebControls" Assembly="Microsoft.Web.UI.WebControls" %>
行 2：  <%@ Control Language="c#" AutoEventWireup="false" Codebehind="simplenews.ascx.cs" Inherits="cmis.Webs.usercontrol.simplenews" TargetSchema="http://schemas.microsoft.com/intellisense/ie5" %>
行 3：  <DIV style="WIDTH: 411px; POSITION: relative; HEIGHT: 189px" ms_positioning="GridLayout">
 源文件: c:\inetpub\wwwroot\Webs\simplenews.ascx    行: 1 程序集加载跟踪: 下列信息有助于确定程序集“Microsoft.Web.UI.WebControls”无法加载的原因。
=== Pre-bind state information ===
LOG: DisplayName = Microsoft.Web.UI.WebControls
 (Partial)
LOG: Appbase = file:///c:/inetpub/wwwroot/Webs
LOG: Initial PrivatePath = bin
Calling assembly : (Unknown).
===LOG: Policy not being applied to reference at this time (private, custom, partial, or location-based assembly bind).
LOG: Post-policy reference: Microsoft.Web.UI.WebControls
LOG: Attempting download of new URL file:///C:/WINNT/Microsoft.NET/Framework/v1.1.4322/Temporary ASP.NET Files/webs/8c760a76/649fbc87/Microsoft.Web.UI.WebControls.DLL.
LOG: Attempting download of new URL file:///C:/WINNT/Microsoft.NET/Framework/v1.1.4322/Temporary ASP.NET Files/webs/8c760a76/649fbc87/Microsoft.Web.UI.WebControls/Microsoft.Web.UI.WebControls.DLL.
LOG: Attempting download of new URL file:///c:/inetpub/wwwroot/Webs/bin/Microsoft.Web.UI.WebControls.DLL.
LOG: Attempting download of new URL file:///c:/inetpub/wwwroot/Webs/bin/Microsoft.Web.UI.WebControls/Microsoft.Web.UI.WebControls.DLL.
LOG: Attempting download of new URL file:///C:/WINNT/Microsoft.NET/Framework/v1.1.4322/Temporary ASP.NET Files/webs/8c760a76/649fbc87/Microsoft.Web.UI.WebControls.EXE.
LOG: Attempting download of new URL file:///C:/WINNT/Microsoft.NET/Framework/v1.1.4322/Temporary ASP.NET Files/webs/8c760a76/649fbc87/Microsoft.Web.UI.WebControls/Microsoft.Web.UI.WebControls.EXE.
LOG: Attempting download of new URL file:///c:/inetpub/wwwroot/Webs/bin/Microsoft.Web.UI.WebControls.EXE.
LOG: Attempting download of new URL file:///c:/inetpub/wwwroot/Webs/bin/Microsoft.Web.UI.WebControls/Microsoft.Web.UI.WebControls.EXE.
请教高手啊