Please refer to the attached sample project. After running it, the following error is observed:
************** Exception Text ************** System.NullReferenceException: Object reference not set to an instance of an object. at Telerik.WinControls.UI.RadPictureBoxElement.UpdateParentControl() at Telerik.WinControls.UI.RadPictureBoxElement.OnParentChanged(RadElement previousParent) at Telerik.WinControls.RadElement.SetParent(RadElement parent) at Telerik.WinControls.RadElement.ChangeCollection(RadElement child, ItemsChangeOperation changeOperation) at Telerik.WinControls.RadElementCollection.OnInsertComplete(Int32 index, Object value) at System.Collections.CollectionBase.System.Collections.IList.Add(Object value) at Telerik.WinControls.RadElementCollection.Add(RadElement value) at _1574930GanttCustomDataItem.RadForm1.customGanttViewTextViewCellElement.CreateChildElements() in C:\Projects\1574930GanttCustomDataItem\1574930GanttCustomDataItem\RadForm1.vb:line 75 at Telerik.WinControls.RadElement.CallCreateChildElements() at Telerik.WinControls.RadElement.Construct() at Telerik.WinControls.RadElement..ctor() at Telerik.WinControls.RadItem..ctor() at Telerik.WinControls.UI.GanttViewTextViewCellElement..ctor(GanttViewTextItemElement owner, GanttViewTextViewColumn column) at _1574930GanttCustomDataItem.RadForm1.customGanttViewTextViewCellElement..ctor(GanttViewTextItemElement owner, GanttViewTextViewColumn column) in C:\Projects\1574930GanttCustomDataItem\1574930GanttCustomDataItem\RadForm1.vb:line 59 at _1574930GanttCustomDataItem.RadForm1.radGanttView1_DataCellElementCreating(Object sender, GanttViewDataCellElementCreatingEventArgs e) in C:\Projects\1574930GanttCustomDataItem\1574930GanttCustomDataItem\RadForm1.vb:line 51 at Telerik.WinControls.UI.RadGanttViewElement.OnDataCellCreating(GanttViewDataCellElementCreatingEventArgs e) at Telerik.WinControls.UI.GanttViewTextViewCellElementProvider.CreateElement(GanttViewTextViewColumn data, Object context) at Telerik.WinControls.UI.BaseVirtualizedElementProvider`1.GetElement(T data, Object context) at Telerik.WinControls.UI.BaseVirtualizedContainer`1.UpdateElement(Int32 position, T data) at Telerik.WinControls.UI.BaseVirtualizedContainer`1.MeasureElements() at Telerik.WinControls.UI.BaseVirtualizedContainer`1.MeasureOverride(SizeF availableSize) at Telerik.WinControls.RadElement.MeasureCore(SizeF availableSize) at Telerik.WinControls.RadElement.Measure(SizeF availableSize) at Telerik.WinControls.UI.LightVisualElement.MeasureElements(SizeF availableSize, SizeF clientSize, Padding borderThickness) at Telerik.WinControls.UI.LightVisualElement.MeasureOverride(SizeF availableSize) at Telerik.WinControls.RadElement.MeasureCore(SizeF availableSize) at Telerik.WinControls.RadElement.Measure(SizeF availableSize) at Telerik.WinControls.UI.VirtualizedStackContainer`1.MeasureElementCore(RadElement element, SizeF availableSize) at Telerik.WinControls.UI.VirtualizedStackContainer`1.MeasureElement(IVirtualizedElement`1 element) at Telerik.WinControls.UI.BaseVirtualizedContainer`1.MeasureElements() at Telerik.WinControls.UI.BaseVirtualizedContainer`1.MeasureOverride(SizeF availableSize) at Telerik.WinControls.RadElement.MeasureCore(SizeF availableSize) at Telerik.WinControls.RadElement.Measure(SizeF availableSize) at Telerik.WinControls.UI.GanttViewTextViewElement.MeasureOverride(SizeF availableSize) at Telerik.WinControls.RadElement.MeasureCore(SizeF availableSize) at Telerik.WinControls.RadElement.Measure(SizeF availableSize) at Telerik.WinControls.UI.RadGanttViewElement.MeasureOverride(SizeF availableSize) at Telerik.WinControls.RadElement.MeasureCore(SizeF availableSize) at Telerik.WinControls.RadElement.Measure(SizeF availableSize) at Telerik.WinControls.RootRadElement.MeasureOverride(SizeF availableSize) at Telerik.WinControls.RootRadElement.MeasureCore(SizeF availableSize) at Telerik.WinControls.RadElement.Measure(SizeF availableSize) at Telerik.WinControls.RadElementTree.PerformInnerLayout(Boolean performMeasure, Int32 x, Int32 y, Int32 width, Int32 height) at Telerik.WinControls.RadControl.OnLoad(Size desiredSize) at Telerik.WinControls.RadControl.LoadElementTree(Size desiredSize) at Telerik.WinControls.RadControl.OnCreateControl() at System.Windows.Forms.Control.CreateControl(Boolean fIgnoreVisible) at System.Windows.Forms.Control.CreateControl(Boolean fIgnoreVisible) at System.Windows.Forms.Control.CreateControl() at System.Windows.Forms.Control.WmShowWindow(Message& m) at System.Windows.Forms.Control.WndProc(Message& m) at System.Windows.Forms.ScrollableControl.WndProc(Message& m) at System.Windows.Forms.Form.WmShowWindow(Message& m) at System.Windows.Forms.Form.WndProc(Message& m) at Telerik.WinControls.UI.RadFormControlBase.WndProc(Message& m) at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m) at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m) at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam) ************** Loaded Assemblies **************
Workaround: set the RadOictureBoxElement.PanelDisplayMode property to PictureBoxPanelDisplayMode.None.