为什么axpx.vb中总提示“未声明名称Check1”


<%@ Page Language="VB" AutoEventWireup="false" CodeFile="testdb.aspx.vb" Inherits="testdb" %><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<%@ Import Namespace="System.Data.OleDb" %>
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
    <title>无标题页</title>
</head>
<body>
    <form id="Form1" runat="server">
    <div>
        <table border="0" cellspacing="0" cellpadding="0" width="100%">
            <tr>
                <td>
                    <asp:Label ID="Label1" runat="server" Text="选择："></asp:Label>
                    <asp:LinkButton ID="SelectAll" runat="server">全选</asp:LinkButton>-
                    <asp:LinkButton ID="unSelectAll" runat="server">反选</asp:LinkButton>
                </td>
            </tr>
            <tr>
                <asp:Repeater ID="customers" runat="server">
                    <HeaderTemplate>
                        <table border="1" width="100%">
                            <tr>
                                <th>
                                    选择
                                </th>
                                <th>
                                    Title
                                </th>
                                <th>
                                    LinkUrl
                                </th>
                                <th>
                                    CreateTime
                                </th>
                                <th>
                                    操作
                                </th>
                            </tr>
                    </HeaderTemplate>
                    <ItemTemplate>
                        <tr>
                            <td>
                                <asp:CheckBox ID="Check1" runat="server" />
                            </td>
                            <td>
                                <%#Container.DataItem("Title")%>
                            </td>
                            <td>
                                <asp:HyperLink ID="HyperLink3" runat="server" NavigateUrl='<%#Container.DataItem("LinkUrl")%>'><%#Container.DataItem("LinkUrl")%></asp:HyperLink>
                            </td>
                            <td>
                                <%#Container.DataItem("CreateTime")%>
                            </td>
                            <td>
                                <asp:HyperLink ID="HyperLink1" runat="server">查看</asp:HyperLink>
                                <asp:HyperLink ID="HyperLink2" runat="server">审核</asp:HyperLink>
                            </td>
                        </tr>
                    </ItemTemplate>
                    <FooterTemplate>
                        </table>
                    </FooterTemplate>
                </asp:Repeater>
            </tr>
            <tr>
                <td>
                </td>
            </tr>
        </table>
    </div>
    </form>
</body>
</html>
[code=VB.NET]
Protected Sub selectall_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles SelectAll.Click
        Check1.Checked = True    End Sub[/code]