I've scanned the threads in this forum and I'm still stumped on a desig
time issue.  I'm relatively new to .Net Forms development so I may b
overlooking something simple.

I am trying to create a custom UserControl which contains anothe
custom control that is an extension of TextBox.  The custom TextBox an
the parent control I want to place it inside of are both in the sam
assembly (dll).  At design time, when I drop the custom TextBox insid
of the custom UserControl VS (2003 .Net 1.1) complains with - "Th
specified cast is not valid."  I'm assuming this occurs when th
designer attempts to instantiate the custom TextBox.

I created another custom TextBox that extends TextBox and nothing else
This control does not create a problem for VS when used as describe
above.

Here is the source for the custom TextBox that is causing a problem.  
am showing only the public properties, constructor and designer relate
logic.  This class also overrides a number of event handlers to handl
keypress validation at runtime.  I left this code out - I can't imagin
this logic would present any design time issues.

using System;
using System.Windows.Forms;
using log4net;
using org.twia.meta;

namespace org.twia.forms
{

/// <summary>
/// Supplies the list of modes to be used by the control.
/// </summary>
public enum MaskMode
{
KeyPress,
Leave
}

/// Text Box control for use in a Model View Mediator GUI.
/// </summary>
public class MVMTextBox : System.Windows.Forms.TextBox
ValidatingControl
    {

private bool supportsValidation = false;
private ControlBindingType bindingType
ControlBindingType.None;
private static readonly ILog log
LogManager.GetLogger(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType);

// validation specific properties
private System.Windows.Forms.ErrorProvider errorProvider = ne
System.Windows.Forms.ErrorProvider();
internal string mask = string.Empty;    //regular expression mask
internal bool stripMask = true; //strip mask before validation
internal string text = string.Empty;    //actual text with mas
characters removed
internal int selectionStart = 0; //current position in _text
internal string sampleInput = string.Empty; //sample input t
complete regular expression fields for keypress validation
private MaskMode mode = MaskMode.Leave;
/// <summary>
/// Required designer variable.
/// </summary>
private System.ComponentModel.IContainer components = null;

public MVMTextBox()
{
// This call is required by the Windows.Forms Form Designer.
InitializeComponent();

// TODO: Add any initialization after the InitializeComponen
call

}

// Properties
/// <summary>
/// Public property used to expose the mask mode of the control.
/// </summary>
public MaskMode Mode
{
get { return mode; }
set { mode = value; }
}
       
/// <summary>
/// property encapsulating the mask
/// </summary>
public string Mask
{
get { return mask; }
set
{
mask = value != null ? value : "";
renderMaskedText(text);
}
}

/// <summary>
/// property encapsulating actual unmasked text
/// </summary>
public string UnmaskedText
{
get
{
if (stripMask)
return text;
else
return Text;
}
set
{
text = value != null ? value : "";
renderMaskedText(text);
}
}

#region Internal Methods

/// <summary>
/// property encapsulating errorProvider
/// </summary>
internal string Error
{
set
{
errorProvider.SetError(this, value);
}
}

#endregion

/// <summary>
/// Clean up any resources being used.
/// </summary>
protected override void Dispose( bool disposing )
{
if( disposing )
{
if (components != null)
{
components.Dispose();
}
}
base.Dispose( disposing );
}

#region Component Designer generated code
/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeComponent()
{
components = new System.ComponentModel.Container();
}
#endregion

    }
}

Could this be an issue with initialization/serialization of the publi
properties?  I tried making the properties non-public and still had the
same problem.

If you can point me in the right direction to solving this problem -
thanks!

John