Ok, I've downloaded the code and looked in the erata.

I've been stuck on this for hours, and the code doesn't work.

I click the button and I still only get the javascript popup "please enter a number" or "the data is valid".

The below code doesn't set the .Text property like it should:

    Protected Sub Button1_Click(ByVal sender As Object, _
                                ByVal e As System.EventArgs)
        Me.WebCustomControl1_1.Text = "CustomControl"
        Me.TextBox1.Text = "StandardTextbox"
    End Sub





The paragragh on page 892 also says "Click the 'Populate' button" and "Click the 'Postback' button"

but there are NO 'Populate' or 'Postback' buttons! in the page or downloaded code! :(

here's the control code:

Imports System.ComponentModel
Imports System.Web.UI

<DefaultProperty("Text"), _
 ToolboxData("<{0}:WebCustomControl1 runat=server></{0}:WebCustomControl1>")> _
Public Class WebCustomControl1
    Inherits System.Web.UI.WebControls.WebControl
    Implements System.Web.UI.ICallbackEventHandler

    Dim _text As String

    <Bindable(True), Category("Appearance"), DefaultValue(""), Themeable(False)> _
    Property [Text]() As String
        Get
            _text = CStr(ViewState("ControlText"))
            If (_text = Nothing) Then
                Return String.Empty
            End If

            Return _text
        End Get

        Set(ByVal Value As String)
            ViewState("ControlText") = Value
        End Set
    End Property




    Protected Overrides Sub Render(ByVal output As System.Web.UI.HtmlTextWriter)
        output.RenderBeginTag(HtmlTextWriterTag.Div)

        output.AddAttribute(HtmlTextWriterAttribute.Type, "text")
        output.AddAttribute(HtmlTextWriterAttribute.Id, Me.ClientID)
        output.AddAttribute(HtmlTextWriterAttribute.Name, Me.ClientID)
        output.AddAttribute(HtmlTextWriterAttribute.Value, Me.Text)

        output.AddAttribute("OnBlur", "ClientCallback();")
        Me.AddAttributesToRender(output)

        output.RenderBeginTag(HtmlTextWriterTag.Input)
        output.RenderEndTag()

        output.RenderEndTag()
    End Sub

    Protected Overrides Sub OnPreRender(ByVal e As System.EventArgs)
        '23-22 Detect Browser
        If (Page.Request.Browser.EcmaScriptVersion.Major > 0) Then

            Page.ClientScript.RegisterClientScriptInclude( _
                "UtilityFunctions", "JScript.js")

            Page.ClientScript.RegisterStartupScript(GetType(Pa ge), _
               "ControlFocus", "document.getElementById('" & Me.ClientID & "').focus();", _
               True)

            Page.ClientScript.RegisterStartupScript( _
                GetType(Page), "ClientCallback", _
                "function ClientCallback() {" & _
                    "args=document.getElementById('" & Me.ClientID & "').value;" & _
                    Page.ClientScript.GetCallbackEventReference(Me, "args", _
                        "CallbackHandler", Nothing, "ErrorHandler", True) + "}", _
                True)
        End If
    End Sub


    Public Sub RaiseCallbackEvent(ByVal eventArgument As String) Implements System.Web.UI.ICallbackEventHandler.RaiseCallbackE vent
        Dim result As Int32
        If (Not Int32.TryParse(eventArgument, result)) Then
            Throw New Exception("The method or operation is not implemented.")
        End If
    End Sub

    Public Function GetCallbackResult() As String Implements ICallbackEventHandler.GetCallbackResult
        Return "Valid Data"
    End Function

End Class

Finally found it.

the aspx file 'OnClick=' was missing, should be:

<asp:Button ID="Button1" runat="server" Text="Populate" OnClick="Button1_Click" />