Styan,
I get an error when I try to copy and paste a node on the diagram. When I copy the debug info seems like it has copied the object, but i cant say for sure. the 
currentDiagram.PasteSelection(copyData, 10, 10); throws this exception:

{MS.Internal.WrappedException: Catastrophic failure (Exception from HRESULT: 0x8000FFFF (E_UNEXPECTED)) ---> System.Exception: Catastrophic failure (Exception from HRESULT: 0x8000FFFF (E_UNEXPECTED))
   at MS.Internal.XcpImports.CheckHResult(UInt32 hr)
   at MS.Internal.XcpImports.FrameworkElement_MeasureOverride(FrameworkElement element, Size availableSize)
   at System.Windows.FrameworkElement.MeasureOverride(Size availableSize)
   at System.Windows.Controls.Canvas.MeasureOverride(Size constraint)
   at System.Windows.FrameworkElement.MeasureOverride(IntPtr nativeTarget, Single inWidth, Single inHeight, Single& outWidth, Single& outHeight)
   --- End of inner exception stack trace ---}

Please let me kow what other information you would like me send over to debug and trace the source of the problem.

any help would be appreciated,
Thanks, Don Almeida.

it is a container node with two children
1) a Control Node that has a TextBlock and
2) a shapenode.

These are the properties that are used.
public TaskNode(Diagram diagram, Task task, Flow flow, UserMapPreferences preferences)
       {
           const int SUBSCRIPTIONID = -1;
           const bool ISPROPERTIESEDITABLE = true;

           Preferences = preferences;
           FlowDiagram = diagram;
           FlowTask = task;
           Flow = flow;
           Brush anchorBrush = Brushes.White;
           AnchorPattern anchorPattern = new AnchorPattern(new AnchorPoint[]
               {
                   new AnchorPoint(50, 0, true, true, anchorBrush, 1),
                   new AnchorPoint(100, 50, true, true, anchorBrush, 2),
                   new AnchorPoint(50, 100, true, true, anchorBrush, 3),
                   new AnchorPoint(0, 50, true, true, anchorBrush, 4)
               });
           TextBlock taskText = new TextBlock
           {
               FontSize = 12,
               Text = TaskHelper.GetTaskText(FlowTask, Preferences),
               TextAlignment = TextAlignment.Center,
               Margin = new Thickness(0, 0, 0, 0),
               TextWrapping = TextWrapping.Wrap,
               UseLayoutRounding = true,
           };
           ControlNode cn = new ControlNode(FlowDiagram, taskText)
           {
               Bounds = new Rect(FlowTask.XLocation - 100 + 16, FlowTask.YLocation + 30, 200, 25),
               EnabledHandles = AdjustmentHandles.None,
               Locked = true,
           };
           string imageUri = task.Image > 0 ? string.Format(DiagramHelper.GetBaseUrl() + CustomImageHandler, task.Image) : TaskHelper.GetImageUrl(FlowTask);
           ShapeNode node = new ShapeNode(FlowDiagram)
           {
               Bounds = new Rect(FlowTask.XLocation, FlowTask.YLocation, 32, 32),
               Image = new BitmapImage(new Uri(imageUri, UriKind.RelativeOrAbsolute)),
               ImageAlign = ImageAlign.Center,
               Transparent = true,
               Pen = new Pen(Brushes.Black),
               Tag = new TaskNodeTag(FlowTask, SUBSCRIPTIONID, flow, ISPROPERTIESEDITABLE, cn),
               BorderBrush = new SolidColorBrush(Colors.Black),
               BorderThickness = new Thickness(1, 1, 1, 1),
               AnchorPattern = anchorPattern,
               Locked = true,
           };
           TaskImageNode = node;
           TaskTextNode = cn;
           var transparent = new SolidColorBrush(Colors.Transparent);
           Node = new ContainerNode(diagram)
           {
               Bounds = new Rect(FlowTask.XLocation, FlowTask.YLocation, 32, 32),
               Transparent = false,
               BorderThickness = new Thickness(0, 0, 0, 0),
               AllowIncomingLinks = true,
               AllowOutgoingLinks = true,
               Pen = new Pen(transparent, 1),
               EnabledHandles = AdjustmentHandles.Move,
               AllowAddChildren = true,
               AllowRemoveChildren = false
           };
           if (task.Type == TaskType.Start)
           {
               Node.AllowIncomingLinks = false;
               Node.AllowOutgoingLinks = true;
           }
           Node.Children.Add(TaskImageNode);
           Node.Children.Add(TaskTextNode);
       }

thanks for the pointers I will look at the tutorial.
I wil prepare the Project and send it over.. However what code did you use to copy paste..

This is what i am doing.. one funciton is called int he copy menuitem command event handler and the other is on the paste menuitem event handler.
SelectionCopy copy = null;
private void CopySelection()
       {
           copy = currentDiagram.CopySelection(false);
           SetStatusMessage("Item Selected", Brushes.White);
       }

private void PasteSelection()
       {
           if (copy != null)
           {
               currentDiagram.PasteSelection(copy, 10, 10);
           }
       }

I have managed to reproduce the problem in a sample applicaiotn and i have sent it over to support@mindfusion.eu

Thanks, Don Almeida

This might sound dumb but is Diagramlite 1.4 the latest release for silverlight or  MindFusion.Diagramming for Silverlight V1.3 the lates version for silverlight. I currently have this build number.. 1.3.0.21960 for MindFusion.Diagramming.Silverlight.dll but before this version I used DiagramLite.dll with version 1.2.0.24983.
What version should I upgrade to?

Thanks Stoyan for the link.. is it possble to add a a new feature like raise an event whenever a user copies or pastes an object (also Redo/Undo). Currently I will write my own delegate/Event handler as I need to update many other controls (Treeview etc.) when the user copies/pastes/ Undo/Redos an operation.

You guys are awesome, thanks Don Almeida

Thank you Stoyan.