C # You can not implicitly convert a value of an attribute of a class

XML file with the parsing of a document based on constituents which can have nested nodes (sub-trees of any depth).

<document>
  <wordcount>181</wordcount>
  <cputime>0.084678</cputime>
  <paragraph>
    <sentence id="1">
      <token begin="4" ctag="DA" end="6" form="El" gen="masculine" id="t1.1" lemma="el" num="singular" phon="el" pos="determiner" tag="DA0MS0" type="article">
       <morpho>
         <analysis ctag="DA" gen="masculine" lemma="el" num="singular" pos="determiner" selected="1" tag="DA0MS0" type="article"/>
       </morpho>
      </token>
  <constituents>
    <node head="1" label="grup-verb">
      <node label="sn">
        <node label="espec-ms">
          <node head="1" label="j-ms">
            <node head="1" leaf="1" token="t1.1" word="El"/></node>
        </node>
        <node head="1" label="grup-nom-ms">
          <node head="1" label="n-ms">
            <node head="1" leaf="1" token="t1.2" word="doctor"/></node>
          <node label="w-ms">
            <node head="1" leaf="1" token="t1.3" word="Fergusson"/></node>
        </node>
      </node>
  </sentence>
 </paragraph>
</document>

I have defined the Classes structure for the structure of the XML (generated by freeling with CoNLL format).

public class Senses
{
    [XmlElement(ElementName = "sense")]
    public List<Sense> Sense { get; set; }
}

[XmlRoot(ElementName = "node")]
public class Node
{
    [XmlAttribute(AttributeName = "head")]
    public string Head { get; set; }
    [XmlAttribute(AttributeName = "leaf")]
    public string Leaf { get; set; }
    [XmlAttribute(AttributeName = "token")]
    public string Token { get; set; }
    [XmlAttribute(AttributeName = "word")]
    public string Word { get; set; }
    [XmlElement(ElementName = "node")]
    public List<Node> Nodo { get; set; }
    [XmlAttribute(AttributeName = "label")]
    public string Label { get; set; }
}

[XmlRoot(ElementName = "constituents")]
public class Constituents
{
    [XmlElement(ElementName = "node")]
    public Node Node { get; set; }
}

[XmlRoot(ElementName = "sentence")]
public class Sentence
{
    [XmlElement(ElementName = "token")]
    public List<Token> Token { get; set; }
    [XmlElement(ElementName = "constituents")]
    public Constituents Constituents { get; set; }
    [XmlAttribute(AttributeName = "id")]
    public string Id { get; set; }
}

[XmlRoot(ElementName = "paragraph")]
public class Paragraph
{
    [XmlElement(ElementName = "sentence")]
    public List<Sentence> Sentence { get; set; }
}

When loading the XML file with an Enumerator and LINQ, it generates the message "Unable to convert the System.Collections.Generic.IEnumerable type in Project.Node implicitly. An explicit conversion already exists (check if a conversion is missing) " I have used ToList () conversion but the error continues. At the foot I send the code of the load. Thank you in advance for the help.

            XDocument docuXML = XDocument.Parse(TxtCodificado);

            // Carga el archivo y reconoce vocales asentuadas del Español y símbolos. Se debe preveer el lenguaje del texto para
            archivoXML.LoadXml(TxtCodificado);

            IEnumerable<Paragraph> Parrafos = docuXML.Root.Descendants("paragraph")
                .Select(Parrafs => new Paragraph
                {
                    Sentence = Parrafs.Elements("sentence")
                    .Select(Sentencs => new Sentence
                    {
                        Id = (string)Sentencs.Attribute("id"),
                        Token = Sentencs.Elements("token")
                        .Select(complex => new Token
                        {
                            Begin = (string)complex.Attribute("begin"),
                            End = (string)complex.Attribute("end"),
                            Form = (string)complex.Attribute("form"),
                            Gen = (string)complex.Attribute("gen"),
                            Id = (string)complex.Attribute("id"),
                            Case = (string)complex.Attribute("case"),
                            Ctag = (string)complex.Attribute("ctag"),
                            Lemma = (string)complex.Attribute("lemma"),
                            Person = (string)complex.Attribute("person"),
                            Phon = (string)complex.Attribute("phon"),
                            Pos = (string)complex.Attribute("pos"),
                            Tag = (string)complex.Attribute("tag"),
                            Type = (string)complex.Attribute("type"),
                        }).ToList(),
                        Constituents = Sentencs.Elements("constitutens")
                        .Select(constitu => new Constituents
                            {
                                Node = constitu.Elements("node")
                                .Select(Nd => new Node
                                {
                                    Head = (string)Nd.Attribute("head"),
                                    Leaf = (string)Nd.Attribute("leaf"),
                                    Token = (string)Nd.Attribute("token"),
                                    Word = (string)Nd.Attribute("word"),
                                    Label = (string)Nd.Attribute("label"),
                                    Nodo = Nd.Elements("node")
                                    .Select(Nod => new Node
                                    {
                                        Leaf = (string)Nod.Attribute("leaf"),
                                        Token = (string)Nod.Attribute("token"),
                                        Word = (string)Nod.Attribute("word"),
                                        Label = (string)Nod.Attribute("label"),
                                        Head = (string)Nod.Attribute("head"),
                                    }).ToList()
                                })
                            }).ToList()
                    }).ToList()
                });
            return Parrafos.ToList();