Compilation Error after modifying.aspx.vb code

Hi,
I have a webapp that was originally built using framework 1.1 and I need to make some changes to the code behind (aspx.vb).
When I make the simplest of changes (eg, adding a comment), then I get a compile error when trying to access the associate web page.
I seem to recall a similar problem when we made changes to other pages a few years ago, but cannot remember what the cause/solution was. Although I think it had something to do with the code at the top of the pages.
Top of "LeaveRequest.aspx"....
<%@ Page Language="vb" AutoEventWireup="false" Inherits="LeaveRequest" trace="false" Codefile="LeaveRequest.aspx.vb" %>
<%@ Register TagPrefix="Menu" TagName="MenuBar" Src="~/MeunBar.ascx" %>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD runat="server">
Top of "LeaveRequest.aspx.vb"....
...