>private void _AddPanel(string sKey) >{ > UserControl control; > > switch (sKey) > { > case "ship_items": > control = new crlShipItems(); > > this.Controls.Add(control); Try changing this.Controls.Add to: <pre> this.Controls.Add((UserControl)control);You may also need to cast the .Left/Top control (or create another reference to the same object with it already cast to the UserControl type).