osea mi codigo quedo asi
<html>
<head>
</head>
<body>
<form runat="server">
<form id="Form1" runat="server" method="post">
<asp:checkboxlist id="cbList" runat="server" RepeatColumns="3" RepeatDirection="Horizontal" TextAlign="Right" AutoPostBack="True" OnSelectedIndexChanged="Check_Clicked">
<asp:ListItem>Web Site News</asp:ListItem>
<asp:ListItem>New Products</asp:ListItem>
<asp:ListItem>Job Postings</asp:ListItem>
<asp:ListItem>User Newsletter</asp:ListItem>
<asp:ListItem>Bugs and Updates</asp:ListItem>
</asp:checkboxlist>
<asp:Label id="Message" runat="server">Label</asp:Label>
<p>
</p>
</form>
</form>
</body>
</html
talvez aqui esta el problema, estoy usando webmatrix