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Getting error: <code>Description: An error occurred during the compilation of a resource required to service this request. Please review the following specific error details and modify your source code appropriately.

Compiler Error Message: CS1061: 'System.Web.Mvc.HtmlHelper<object>' does not contain a definition for 'Body' and no extension method 'Body' accepting a first argument of type 'System.Web.Mvc.HtmlHelper<object>' could be found (are you missing a using directive or an assembly reference?)</code> on the <code>body</code> line

    namespace MySite.Helpers
    {
        public static class HtmlHelpers
        {
            public static MvcHtmlString Body(this HtmlHelper htmlHelper)
            {
                string currentControllerName = (string)htmlHelper.ViewContext.RouteData.Values["controller"];
                string currentActionName = (string)htmlHelper.ViewContext.RouteData.Values["action"];
                string css = currentControllerName + "-" + currentActionName;
                var body = new TagBuilder("body");
                body.AddCssClass(css);
                return MvcHtmlString.Create(body.ToString(TagRenderMode.StartTag));
            }
        }

    }

~/Views/Shared/Site.Master:

    <%@ Master Language="C#" Inherits="System.Web.Mvc.ViewMasterPage" %>

    <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
    <html xmlns="http://www.w3.org/1999/xhtml">
    <head runat="server">
        <title><asp:ContentPlaceHolder ID="TitleContent" runat="server" /></title>
        <link href="../../Content/Site.css" rel="stylesheet" type="text/css" />
    </head>

    <body id="argh" class="<%= Html.Body() %>">