Custom Server Controls :: Implementing An Interface From A Class Library In A Custom Control?

I'm building an n-tier application, with the web client and the class library separate. I'm also using the factory pattern of development, using interfaces to act as containers for different objects they are associated with. The problem I'm expreriencing is that I declared a public interface class in the class library and I can create an instance of it in in my aspx pages but whenever I declare it in my custom control code-side, i get an error, like so:

Error 20 The type or namespace name 'IContentMaker' could not be found (are you missing a using directive or an assembly reference?)

notge that I have inherited the class library namespace using the 'using' keyword just in case you are wondering. My code is like so:

using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using TQO_Classes ; //importing the class library project
public partial class PageContentMgr : System.Web.UI.UserControl
{
private IContentMaker _data; //this line throws the error, it works fine on aspx pages