Hello!
I have the very strange problem. Some times (for example when I creates node by drag and drop) I can't delete node by Delete key. I have 2 event handlers for the Diagram object: NodeDeleting and KeyDown. When I press Delete I don't go to them. But when I press Esc I go to the KeyDown event handler. Why is it may be?
P.S.: when I create the node I use the NodeAdapter. Code is below:

private void OnDiagram_NodeCreated(object sender, NodeEventArgs e)
        {
            if (e.Node is DiagramNodeAdapter)
            {
                DiagramNodeAdapter adapter = e.Node as DiagramNodeAdapter;
                TPDENode tpdeNode = new TPDENode();
                NodeType nType = (NodeType)adapter.Tag;
                if (nType == NodeType.SimpleProcess)
                    tpdeNode = new TechnologicalOperation();
                else if (nType == NodeType.ComplexProcess)
                    tpdeNode = new OperationGroupNode();
                else if (nType == NodeType.Bus)
                    tpdeNode = new BusNode();
                else if (nType == NodeType.Text)
                    tpdeNode = new CommentNode();
                else if (nType == NodeType.Reference)
                    tpdeNode = new ReferenceNode();
                else if (nType == NodeType.Filter)
                    tpdeNode = new FilterNode();
                else
                {
                    m_Diagram.Nodes.Remove(e.Node);
                    return;
                }
                m_Diagram.Nodes.Remove(e.Node);
                m_Diagram.Nodes.Add(tpdeNode);
            }
        }
 

 private void OnDiagram_NodeDeleting(object sender, NodeValidationEventArgs e)
        {
            if (e.Node is TPDENode)
            {
                TPDENode node = e.Node as TPDENode;
                if (node is OperationGroupNode)
                {
                    String sMsg = "Deleting the complex process leads to permanently removing all included processes. Are you sure to delete the complex process?";
                    MessageBoxResult rslt = MessageBox.Show(sMsg, "Warning", MessageBoxButton.YesNo, MessageBoxImage.Warning);
                    if (rslt == MessageBoxResult.No)
                        e.Cancel = true;
                    else m_bRemoveCnfr = true;
                }
                else if (node is InputNode || node is OutputNode || node is BeginNode ||
                    node is EndNode)
                    e.Cancel = true;
            }
        }
 

        private void OnDiagram_KeyDown(object sender, KeyEventArgs e)
        {
            switch (e.Key)
            {
                case Key.Escape:
                    m_Diagram.Selection.Clear();
                    break;
            }
        }
 

No, it is not help me. And I see that when I click on the Node I can't delete it by Delete key. But when I draw selection by mouse and select the node I can delete selected (and active) node by delete key

Yes, but the item of the NodeListView is the StackPanel which each child is consists of Image and TextBlock objects. And when I add into the NodeActivated event handler the string
e.Node.Selected = true;
all works. But the follwoing calls didn't get effect:
e.Node.Focus();
m_Diagram.Focus();