Error 13 Type 'System.Web.UI.ScriptManager' exists in 'c: \ Windows \ assembly \ GAC_MSIL \ System.Web.Extensions \ 1.0.61025.0__31bf3856ad364e35 \ System.Web.Extensions.dll', and in 'c : \ Windows \ assembly \ GAC_MSIL \ System.Web.Extensions \ 3.5.0.0__31bf3856ad364e35 \ System.Web.Extensions.dll
it seems like different framework versions , so I guess I can't use it ?