Sharepoint 2010 - error while trying to access a method in a assembly from custom page layout

I have a publishing custom page layout page and have code something like this -

    <ContentPlaceHolder...>
     <script runat="server">
        void Page_Load(object sender, System.EventArgs e)
        {
          lblTest.Text = RTG.Business.Helper.开发者_JAVA技巧IsUrlFavorite(Request.Url).ToString();
        }
     </script>
     <asp:Label ID="lblTest" runat="Server" />
    </ContentPlaceHolder>

It errors out saying -

The type or namespace name 'Business' does not exist in the namespace 'RTG' (are you missing an assembly reference?)

I have the assembly added to my project and am able to access it from a different user control in this same project. I've tried adding the @Assembly and @Import Namespace tags at the top of the page with no luck.

Does anyone know what I'm doing wrong here?

---

Assembly, which define "RTG" namespace, need to be placed in GAC. It possible by gacutil.exe, by manually drag to "c:\windows\assembly", But most better case is add it to sharepoint package, for automatic deploying. To do this, open package in solution, click advanced, and add assembly from project output.

Good luck!