To reproduce: public Form1() { InitializeComponent(); this.radTreeView1.AllowDragDrop = true; this.radTreeView2.AllowDragDrop = true; for (int i = 0; i < 5; i++) { this.radTreeView1.Nodes.Add("Node1." + i); this.radTreeView2.Nodes.Add("Node2." + i); } this.radTreeView1.ScreenTipNeeded += radTreeView1_ScreenTipNeeded; this.radTreeView2.ScreenTipNeeded += radTreeView1_ScreenTipNeeded; } RadOffice2007ScreenTipElement _screenTip = new RadOffice2007ScreenTipElement(); private void radTreeView1_ScreenTipNeeded(object sender, Telerik.WinControls.ScreenTipNeededEventArgs e) { _screenTip.CaptionLabel.Text = "Caption"; _screenTip.MainTextLabel.Text = "text"; _screenTip.AutoSize = true; e.Delay = 2000; e.Item.ScreenTip = _screenTip; } Steps: 1. Drag a node from the first RadTreeView to the other while the screen-tip is shown for the dragged node. 2. When the screen-tip is about to be hidden, the error occurs. Workaround: private void radTreeView1_DragStarting(object sender, RadTreeViewDragCancelEventArgs e) { if (_screenTip.IsElementVisible) { this.radTreeView1.Behavior.HideScreenTip(); } }