You can put it in Web.Config , which exists in your Views folder. It took me a while to realize that it was a hope that it helped.
<system.web> <controls> <add assembly="System.Web.Mvc, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" namespace="System.Web.Mvc" tagPrefix="mvc" /> <add assembly="AjaxControlToolkit" namespace="AjaxControlToolkit" tagPrefix="ajaxToolkit" /> </controls> </system.web>
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