interface problem

 
I've got an issue with and interface I'm trying to implement.
 
The interface is stored in 
     solutionName
        --> CS
             -->App_Code
                  --> IWizardStep.cs
 
I've got server side code inside a page:
<% Implements Interface = "IWizardStep" %>
 
Whenever I try to build the page, I get the error "Could not load type IWizardStep"
This happens even when the page and interface are located in the same folder
What am I doing wrong?
 
 
 
 
 
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