验证码的问题 - 编程论坛

小弟初学，请问为什么验证会错误？
Default.asp.vb
Partial Class _Default
    Inherits System.Web.UI.Page

    Function RndNum(ByVal VcodeNum)
        Dim Vchar As String = "0，1，2，3，4，5，6，7，8，9，A，B，C，D，E，F，G，H，I，J，K，L，M，N，O，P，Q，R，S，T，U，W，X，Y，Z"
        Dim VcArray() As String = Split(Vchar, "，")
        Dim VNum As String = ""
        Dim i As Byte
        For i = 1 To VcodeNum
            Randomize()
            VNum = VNum & VcArray(Int(35 * Rnd()))
        Next
        Return VNum
    End Function
    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        Dim VNUM As String
        Response.Cookies("VNUM").Value = RndNum(4)
        VNUM = Request.Cookies("VNUM").Value
        Label1.Text = VNUM

    End Sub

    Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
        If TextBox1.Text = Label1.Text.ToLower Then
            Label3.Text = "用户您好，欢迎登陆我是范范饭"
        Else
            Label3.Text = "验证码错误啦！！！"
        End If
    End Sub
End Class

Default.aspx

<%@ Page Language="VB" AutoEventWireup="false" CodeFile="Default.aspx.vb" Inherits="_Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.

<html xmlns="http://www. >
<head id="Head1" runat="server">
    <title>无标题页</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        验证码：<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
        <asp:Label ID="Label1" runat="server" Width="176px"></asp:Label>
        <br />
        <asp:Button ID="Button1" runat="server" Text="Button" />
        <br />
        <asp:Label ID="Label3" runat="server" ForeColor="Lime" Height="96px" Width="384px"></asp:Label>
        </div>
    </form>
</body>
</html>