Why can't my user-defined control find it's parts?

I have a user control in a asp.net 2008 app defined as:

<%@ Control Language="VB" AutoEventWireup="false" codefile="DateSelector.ascx.vb"
    Inherits="Controls_DateSelector" %>

<script language="JavaScript1.2" type="text/javascript" src="<%# controlFolderLoc %>/calendar1-82.js"></script>

<asp:Panel ID="Panel1" runat="server" Height="21px" Width="125px">
    <asp:TextBox ID="myDateBox" runat="server" Width="85px"></asp:TextBox>
    <a href="#" onclick="show_calendar('<%# textControlName %>',null,'','MM/dd/YYYY','','<%# customStringOrName %>')">
        Date</a>
</asp:Panel>

and the code file has:

Imports System.Configuration.ConfigurationManager
Imports System.Drawing
Imports HARM

Partial Class Controls_DateSelector
      Inherits System.Web.UI.UserControl

    Protected Const nameOfSubControl As String = "myDateBox"
      Private pparentFormName As String
      Private poutputName As String
      Private pcustomString As String
      Public ReadOnly Property dateSelected() As Date
            Get
            If myDateBox.Text <> "" Then
                Return CDate(myDateBox.Text)
            Else
                Return Nothing
            End If
            End Get
      End Property
.
.
.

when I try to build this, I get "...error BC30451: Name 'myDateBox' is not declared.".
Sometimes the system shows it in the completion list, sometimes it doesn't...but it will not build...