Code

private void diagram_ValidateAnchorPoint(object sender, LinkValidationEventArgs e)
{
	if (CountLinks(e.Node, e.AnchorIndex, e.Link) > 0)
		e.Cancel = true;
}

private int CountLinks(DiagramNode node, int anchorIndex, DiagramLink skipThisLink)
{
	int c = 0;
	foreach (DiagramLink link in node.IncomingLinks)
	{
		if (link == skipThisLink)
			continue;
		if (link.DestinationAnchor == anchorIndex)
			c++;
	}
	foreach (DiagramLink link in node.OutgoingLinks)
	{
		if (link == skipThisLink)
			continue;
		if (link.OriginAnchor == anchorIndex)
			c++;
	}
return c;
}