It does not work for me.
can anyone help me to overcome this issue?
error CS0433: The type 'System.Web.UI.ScriptManager' exists in both 'c:\Users\username\AppData\Local\Temp\Temporary ASP.NET Files\appname.web\2b4135e5\a028d4b8\assembly\dl3\84ffdd32\6596bf53_b0b0cb01\system.web.extensions.DLL' and 'c:\Windows\assembly\GAC_MSIL\System.Web.Extensions\3.5.0.0__31bf3856ad364e35\System.Web.Extensions.dll'