ya napisal takoe:
<%@ Page language="c#"%>

<script runat="server">
  void Page_Load(object sender, EventArgs e) {
    _myButton.Attributes.Add("onclick",
      "document.forms[0].setAttribute('action','page2.aspx');");
  }
</script>

<form runat="server">
  <asp:Button runat="server" id="_myButton" Text="Click Me"/>
</form>
no na stranice  page2.aspx  - otobrajaetsya mnogo oshibki