protected override void OnClick() { UID dockWinID = new UIDClass(); dockWinID.Value = ThisAddIn.IDs.DockableWindow1; // Use GetDockableWindow directly as we want the client IDockableWindow not the internal class IDockableWindow dockWindow = ArcMap.DockableWindowManager.GetDockableWindow(dockWinID); dockWindow.Show(true); }