Caricatos he intentado puniendo onsubmit= "return false" y me cambia la imagen del imagebutton pero me sigue haciendo la recarga de la pagina.
<asp:ImageButton ID="ImageButton28" runat="server" onsubmit= "return false" ImageUrl="~/imagenes/herziosoff.bmp" style="position: absolute; height: 25px; top: 34px; left: 128px; width: 30px; z-index: 9;"/>
Protected Sub ImageButton28_Click(ByVal sender As Object, ByVal e As System.Web.UI.ImageClickEventArgs) Handles ImageButton28.Click
If (ImageButton28.ImageUrl = "~/imagenes/herziosoff.bmp") Then
ImageButton28.ImageUrl = "~/imagenes/herzioson.bmp"
Else
ImageButton28.ImageUrl = "~/imagenes/herziosoff.bmp"
End If
End Sub