使用Telerik控件时出现Failed to create designer 的解决方法

以下三种方法任选其一。（我用了第三种，前两种未测试）

1. Bin-deploy the design-time assembly
   This solution would work only in case you have not installed RadControls for ASP.NET Ajax using the provided setup program. Assemblies installed by a setup program cannot be removed from GAC until the program is uninstalled. This approach is suitable when using only the dll-s from a zip (be that a hotfix or latest internal build).
   • Remove Telerik.Web.Design.dll from the GAC (this would fail if you have installed RadCotnrols for ASP.NET Ajax via the installer)
   • Copy Telerik.Web.Design.dll to your web site or application and make sure the dll is copied to the bin folder
   • Restart Visual Studio
2. GAC-deploy the control library assembly
   • Add Telerik.Web.UI.dll in the GAC
   • Remove Telerik.Web.UI.dll from your bin folder
   • Make sure you have the following line in your web.config:
     <add assembly="Telerik.Web.UI, Version=2009.1.311.35, Culture=neutral, PublicKeyToken=121FAE78165BA3D4"/>
   • Restart Visual Studio
3. Copy Telerik.Web.UI.dll to c:\Program Files\Microsoft Visual Studio 9.0\Common7\IDE\PublicAssemblies and restart Visual Studio.

来源：http://blogs.telerik.com/atanaskorchev/posts/09-03-06/meet_telerik_web_design_dll.aspx