Hi, Use VS2005 ,set an isMdiContainer form.The above is a menu bar, tool bar, on the left there is a tree. Double-click a tree node, open another interface，access to data in the database. Another interface has a UltraGrid, some labers and some textboxes. Use QTP debugger, there are exceptions： The call real-time (JIT) debugging instead of this dialog box for more information See this message to the end. ************** Exception Text ************** System.NullReferenceException: Object reference not set to an instance of an object . In Infragistics.Win.UIElement.VerifyChildElements (ControlUIElementBase controlElement, Boolean recursive) In Infragistics.Win.UIElement.VerifyChildElements (ControlUIElementBase controlElement, Boolean recursive) In Infragistics.Win.UIElement.VerifyChildElements (ControlUIElementBase controlElement, Boolean recursive) In Infragistics.Win.UIElement.VerifyChildElements (ControlUIElementBase controlElement, Boolean recursive) In Infragistics.Win.UIElement.DrawHelper (Graphics graphics, Rectangle invalidRectangle, Boolean doubleBuffer, AlphaBlendMode alphaBlendMode, Boolean clipText, Boolean forceDrawAsFocused, Boolean preventAlphaBlendGraphics) I don't understand. How do I solve this problem? Thanks!