Hi DNNizens,

found it. Obviously the module is getting inside an update panel when the page is switched to edit mode. Therefore a little statement in the o_n_l_o_a_d event helps:

   AJAX.RegisterPostBackControl(ExportToCsvButton);

BUT: How can I achieve this when I don't want a button - but an entry in the module's action menu? How can I register a postback control there?

      public ModuleActionCollection ModuleActions
      {
         get
         {
            ModuleActionCollection actions = new ModuleActionCollection();
            // ... some other stuff ...
            actions.Add(GetNextActionID(), Localization.GetString("ExportToCsv.Action", LocalResourceFile), "ExportToCsv");
            return actions;
         }
      }

      protected override void OnInit(EventArgs e)
      {
         AddActionHandler(MyActions_Click);
         base.OnInit(e);
      }

     private void MyActions_Click(object sender, ActionEventArgs e)
      {
         switch (e.Action.CommandName)
         {
            // ... some other stuff ...
            case "ExportToCsv":
               // code from above (first post in this thread)
               break;
            default:
               break;
         }
      }

?

Happy DNNing!
Michael