Tente definir o valor de Inherits para o nome da sua classe:
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="usageDisp.aspx.cs" Inherits="WebApplication1.usageDisp" %>
De MSDN :
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="usageDisp.aspx.cs" Inherits="WebApplication1.usageDisp" %>