ObjectDisposedException

hi
this might becuase you are creating your form object at class level and never going to reinitialize it after closing it
when ever we close form it disposes its object so if possible then reinstantiate your form object when ever your open new window

The whole thing is over 2000 lines. Ill show the most important parts:
public class program:System.Windows.Forms.Form{
    Form popup;
    public program(){
        loadPopUp();
        MainMenu menu=new MainMenu();
        MenuItem menu1=new MenuItem("Popup"),item=new MenuItem("Show PopUp");
        menu.MenuItems.Add(menu1);
        menu1.MenuItems.Add(item);
        item.Click+=delegate{
            popup.Show();
        }
       this.Menu=menu;
    }
    void loadPopUp(){
        popup=new Form();
        popup.Size=new Size(200,200);
    }
    [STAThread]static void Main(){
        Application.Run(new program());
    }
}