C# problem Signing XML documents with XAdES

using System;
using System.Collections.Generic;
using System.Text;
using System.Security.Cryptography.Xml;
using System.Xml;

namespace TestProject1
{
    internal sealed class XAdESSignedXml : SignedXml
    {
        private readonly List<dataobject> _dataObjects = new List<dataobject>();
        public const string XadesSignaturePropertiesNamespace = "http://uri.etsi.org/01903/v1.1.1#SignedProperties";

        public XAdESSignedXml(XmlDocument document) : base(document) { }

        public override XmlElement GetIdElement(XmlDocument doc, string id)
        {
            if (String.IsNullOrEmpty(id)) return null;

            XmlElement xmlElement = base.GetIdElement(doc, id);
            if (xmlElement != null) return xmlElement;

            //if (_dataObjects.Count == 0) return null;
            foreach (DataObject dataObject in _dataObjects)
            {
                XmlElement nodeWithSameId = findNodeWithAttributeValueIn(dataObject.Data, "Id", id);
                if (nodeWithSameId != null)
                    return nodeWithSameId;
            }
            if (KeyInfo != null)
            {
                XmlElement nodeWithSameId = findNodeWithAttributeValueIn(KeyInfo.GetXml().SelectNodes("."), "Id", id);
                if (nodeWithSameId != null)
                    return nodeWithSameId;
            }
            return null;
        }
        public new void AddObject(DataObject dataObject)
        {
            base.AddObject(dataObject);
            _dataObjects.Add(dataObject);
        }

        public XmlElement findNodeWithAttributeValueIn(XmlNodeList nodeList, string attributeName, string value)
        {
            if (nodeList.Count == 0) return null;
            foreach (XmlNode node in nodeList)
            {
                XmlElement nodeWithSameId = findNodeWithAttributeValueIn(node, attributeName, value);
                if (nodeWithSameId != null) return nodeWithSameId;
            }
            return null;
        }

        private XmlElement findNodeWithAttributeValueIn(XmlNode node, string attributeName, string value)
        {
            string attributeValueInNode = getAttributeValueInNodeOrNull(node, attributeName);
            if ((attributeValueInNode != null) && (attributeValueInNode.Equals(value))) return (XmlElement)node;
            return findNodeWithAttributeValueIn(node.ChildNodes, attributeName, value);
        }

        private string getAttributeValueInNodeOrNull(XmlNode node, string attributeName)
        {
            if (node.Attributes != null)
            {
                XmlAttribute attribute = node.Attributes[attributeName];
                if (attribute != null) return attribute.Value;
            }
            return null;
        }
    }
}
</dataobject></dataobject>

private string signEracun(string xml, X509Certificate2 certificate)
{
    XmlDocument xmlDoc = new XmlDocument();
    xmlDoc.PreserveWhitespace = false;
    xmlDoc.LoadXml(xml);

    #region signing

    TestProject1.XAdESSignedXml signedXml = new TestProject1.XAdESSignedXml(xmlDoc);
    signedXml.Signature.Id = "SignatureId";

    #region object -> signatureProperties
    XmlElement signaturePropertiesRoot;
    XmlElement qualifyingPropertiesRoot;
    string URI = "http://uri.etsi.org/01903/v1.1.1#";
    qualifyingPropertiesRoot = xmlDoc.CreateElement("xds", "QualifyingProperties", URI);
    qualifyingPropertiesRoot.SetAttribute("Target", "#SignatureId");

    signaturePropertiesRoot = xmlDoc.CreateElement("xds", "SignedProperties", URI);
    signaturePropertiesRoot.SetAttribute("Id", "SignedPropertiesId");

    XmlElement SignedSignatureProperties = xmlDoc.CreateElement("xds", "SignedSignatureProperties", URI);

    XmlElement timestamp = xmlDoc.CreateElement("xds", "SigningTime", URI);
    timestamp.InnerText = DateTime.Now.ToString("yyyy-MM-ddTHH:mm:ss.fffZ"); //2011-09-05T09:11:24.268Z
    SignedSignatureProperties.AppendChild(timestamp);

    XmlElement SigningCertificate = xmlDoc.CreateElement("xds", "SigningCertificate", URI);
    XmlElement Cert = xmlDoc.CreateElement("xds", "Cert", URI);
    XmlElement CertDigest = xmlDoc.CreateElement("xds", "CertDigest", URI);
    SHA1 cryptoServiceProvider = new SHA1CryptoServiceProvider();
    byte[] sha1 = cryptoServiceProvider.ComputeHash(certificate.RawData);
    XmlElement DigestMethod = xmlDoc.CreateElement("xds", "DigestMethod", URI); DigestMethod.SetAttribute("Algorithm", SignedXml.XmlDsigSHA1Url);
    XmlElement DigestValue = xmlDoc.CreateElement("xds", "DigestValue", URI); DigestValue.InnerText = Convert.ToBase64String(sha1);
    CertDigest.AppendChild(DigestMethod);
    CertDigest.AppendChild(DigestValue);
    Cert.AppendChild(CertDigest);

    XmlElement IssuerSerial = xmlDoc.CreateElement("xds", "IssuerSerial", URI);
    XmlElement X509IssuerName = xmlDoc.CreateElement("ds", "X509IssuerName", "http://www.w3.org/2000/09/xmldsig#"); X509IssuerName.InnerText = certificate.IssuerName.Name;
    XmlElement X509SerialNumber = xmlDoc.CreateElement("ds", "X509SerialNumber", "http://www.w3.org/2000/09/xmldsig#"); X509SerialNumber.InnerText = certificate.SerialNumber;
    IssuerSerial.AppendChild(X509IssuerName);
    IssuerSerial.AppendChild(X509SerialNumber);
    Cert.AppendChild(IssuerSerial);

    SigningCertificate.AppendChild(Cert);
    SignedSignatureProperties.AppendChild(SigningCertificate);

    signaturePropertiesRoot.AppendChild(SignedSignatureProperties);
    qualifyingPropertiesRoot.AppendChild(signaturePropertiesRoot);
    DataObject dataObject = new DataObject
    {
        Data = qualifyingPropertiesRoot.SelectNodes("."),
    };
    signedXml.AddObject(dataObject);
    #endregion

    // Add the key to the SignedXml document.
    signedXml.SigningKey = certificate.PrivateKey;

    KeyInfo keyInfo = new KeyInfo();
    KeyInfoX509Data keyInfoX509Data = new KeyInfoX509Data(certificate, X509IncludeOption.ExcludeRoot);
    keyInfo.AddClause(keyInfoX509Data);
    signedXml.KeyInfo = keyInfo;

    //Reference 1
    Reference reference2 = new Reference();
    reference2.Type = "http://www.gzs.si/shemas/eslog/racun/1.5#Racun";
    reference2.Uri = "#data";
    signedXml.AddReference(reference2);

    //Reference 2
    reference2 = new Reference();
    reference2.Type = "http://uri.etsi.org/01903/v1.1.1#SignedProperties";
    reference2.Uri = "#SignedPropertiesId";
    //reference2.AddTransform(new XmlDsigExcC14NTransform());
    signedXml.AddReference(reference2);

    // Compute the signature.
    signedXml.ComputeSignature();

    // Get the XML representation of the signature and save
    // it to an XmlElement object.
    XmlElement xmlDigitalSignature = signedXml.GetXml();

    xmlDoc.DocumentElement.AppendChild(xmlDoc.ImportNode(xmlDigitalSignature, true));
    #endregion

    //check XML signature, return false if dont use transorm in seckont reference
    bool checkSign = signedXml.CheckSignature();

    return xmlDoc.OuterXml;

}