Problem in consecutive node checking program with consecutive attributes?

XmlReaderSettings settings = new XmlReaderSettings();
settings.DtdProcessing = DtdProcessing.Parse;

XDocument xdoc = XDocument.Load(XmlReader.Create("fullfilename.xml", settings));

var cons = xdoc.Descendants("xref")
    .GroupBy(x=>x.Parent)
    .Select(grp=> new
        {
            Parent = grp.Key,
            ConsecutiveNodes = grp.Select((n, i)=> new
                {
                    Index = i+1,
                    Node = n
                }),
            Count = grp.Count()
        })
    .ToList();

Console.WriteLine("3 or more consecutive nodes:");
foreach(var o in cons)
{
    if (o.Count>2)
    {
        Console.WriteLine("{0}", new string('=', 30));
        Console.WriteLine("Found in: {0} ... {1}", o.Parent.ToString().Substring(0,15), o.Parent.ToString().Substring(o.Parent.ToString().Length-15,15));
        Console.WriteLine("{0}", new string('-', 50));
        foreach (var c in o.ConsecutiveNodes)
        {
            //Console.WriteLine("{0}", c.Node);
            Console.WriteLine("Original rid value [{0}] will be replaced with [{1}]", c.Node.Attribute("rid").Value, c.Index);
            c.Node.Attribute("rid").Value = c.Index.ToString();
        }
    }
}

3 or more consecutive nodes:
==============================
Found in: <p>In this stud ... 15]</xref>.</p>
--------------------------------------------------
Original rid value [ref2] will be replaced with [1]
Original rid value [ref3] will be replaced with [2]
Original rid value [ref4] will be replaced with [3]
Original rid value [ref20] will be replaced with [4]
Original rid value [ref3] will be replaced with [5]
Original rid value [ref15] will be replaced with [6]
==============================
Found in: <p>The measurin ... cattering..</p>
--------------------------------------------------
Original rid value [ref11] will be replaced with [1]
Original rid value [ref12] will be replaced with [2]
Original rid value [ref13] will be replaced with [3]
Original rid value [ref4] will be replaced with [4]
Original rid value [T2] will be replaced with [5]