Web service - custom type not deserialized

I'm currently developing an application that access to a web service, a PHP based web service. But I have an issue, one of the method returns a custom type and the system is unable to deserialize the informations. Here is the exception thrown :

Error in deserializing body of reply message for operation 'listeDemandeAcces'.
System.InvalidOperationException: There is an error in XML document (1, 577). --> System.InvalidOperationException: The specified type was not recognized: name
='demande', namespace='http://mysite/acces_net', at <demandes xmlns=''>

Here is the code of my Reference.cs generated via the WSDL of the service :

namespace TDF.OSSExtranet.BusinessProxies.ServiceReference1 {

    [System.CodeDom.Compiler.GeneratedCodeAttribute("System.ServiceModel", "4.0.0.0")]
    [System.ServiceModel.ServiceContractAttribute(Namespace="http://mysite/acces_net", ConfigurationName="ServiceReference1.AccesNetWsdlPortType")]
    public interface AccesNetWsdlPortType {

        [System.ServiceModel.OperationContractAttribute(Action="http://mysite/applications/accesnet/ws/ws_clients.php/list" +
            "eDemandeAcces", ReplyAction="*")]
        [System.ServiceModel.XmlSerializerFormatAttribute(Style=System.ServiceModel.OperationFormatStyle.Rpc, SupportFaults=true, Use=System.ServiceModel.OperationFormatUse.Encoded)]
        [System.ServiceModel.ServiceKnownTypeAttribute(typeof(IntervenantV2))]
        [System.ServiceModel.ServiceKnownTypeAttribute(typeof(Demande))]
        [System.ServiceModel.ServiceKnownTypeAttribute(typeof(Intervenant))]
        [System.ServiceModel.ServiceKnownTypeAttribute(typeof(Projet))]
        [return: System.ServiceModel.MessageParameterAttribute(Name="resultat_req_da")]
        TDF.OSSExtranet.BusinessProxies.ServiceReference1.ResultatReqDa listeDemandeAcces(string login, string password, TDF.OSSExtranet.BusinessProxies.ServiceReference1.RequestDAFilter filter);
    }

    /// <remarks/>
    [System.CodeDom.Compiler.GeneratedCodeAttribute("System.Xml", "4.0.30319.34230")]
    [System.SerializableAttribute()]
    [System.Diagnostics.DebuggerStepThroughAttribute()]
    [System.ComponentModel.DesignerCategoryAttribute("code")]
    [System.Xml.Serialization.SoapTypeAttribute(Namespace="http://mysite/acces_net")]
    public partial class Demande : object, System.ComponentModel.INotifyPropertyChanged {

        private string num_demandeField;

        private System.DateTime date_demandeField;

        private System.DateTime date_maj_demandeField;

        private string statut_dem_accesField;

        private string code_siteField;

        private string code_igField;

        private ZoneInterventionV2 zone_interventionField;

        private System.DateTime date_deb_interventionField;

        private System.DateTime date_fin_interventionField;

        private bool accompagnement_demandeField;

        private bool accompagnement_requisField;

        private string nature_interventionField;

        private string code_projet_TDFField;

        private bool impact_TDFField;

        private bool travaux_dangereuxField;

        private Demandeur demandeurField;

        private IntervenantV2[] intervenantsField;

        private string num_diField;

        private string num_btField;

        /// <remarks/>
        [System.Xml.Serialization.SoapElementAttribute(DataType="integer")]
        public string num_demande {
            get {
                return this.num_demandeField;
            }
            set {
                this.num_demandeField = value;
                this.RaisePropertyChanged("num_demande");
            }
        }

        /// <remarks/>
        public System.DateTime date_demande {
            get {
                return this.date_demandeField;
            }
            set {
                this.date_demandeField = value;
                this.RaisePropertyChanged("date_demande");
            }
        }

        /// <remarks/>
        public System.DateTime date_maj_demande {
            get {
                return this.date_maj_demandeField;
            }
            set {
                this.date_maj_demandeField = value;
                this.RaisePropertyChanged("date_maj_demande");
            }
        }

        /// <remarks/>
        [System.Xml.Serialization.SoapElementAttribute(DataType="integer")]
        public string statut_dem_acces {
            get {
                return this.statut_dem_accesField;
            }
            set {
                this.statut_dem_accesField = value;
                this.RaisePropertyChanged("statut_dem_acces");
            }
        }

        /// <remarks/>
        public string code_site {
            get {
                return this.code_siteField;
            }
            set {
                this.code_siteField = value;
                this.RaisePropertyChanged("code_site");
            }
        }

        /// <remarks/>
        public string code_ig {
            get {
                return this.code_igField;
            }
            set {
                this.code_igField = value;
                this.RaisePropertyChanged("code_ig");
            }
        }

        /// <remarks/>
        public ZoneInterventionV2 zone_intervention {
            get {
                return this.zone_interventionField;
            }
            set {
                this.zone_interventionField = value;
                this.RaisePropertyChanged("zone_intervention");
            }
        }

        /// <remarks/>
        public System.DateTime date_deb_intervention {
            get {
                return this.date_deb_interventionField;
            }
            set {
                this.date_deb_interventionField = value;
                this.RaisePropertyChanged("date_deb_intervention");
            }
        }

        /// <remarks/>
        public System.DateTime date_fin_intervention {
            get {
                return this.date_fin_interventionField;
            }
            set {
                this.date_fin_interventionField = value;
                this.RaisePropertyChanged("date_fin_intervention");
            }
        }

        /// <remarks/>
        public bool accompagnement_demande {
            get {
                return this.accompagnement_demandeField;
            }
            set {
                this.accompagnement_demandeField = value;
                this.RaisePropertyChanged("accompagnement_demande");
            }
        }

        /// <remarks/>
        public bool accompagnement_requis {
            get {
                return this.accompagnement_requisField;
            }
            set {
                this.accompagnement_requisField = value;
                this.RaisePropertyChanged("accompagnement_requis");
            }
        }

        /// <remarks/>
        [System.Xml.Serialization.SoapElementAttribute(DataType="integer")]
        public string nature_intervention {
            get {
                return this.nature_interventionField;
            }
            set {
                this.nature_interventionField = value;
                this.RaisePropertyChanged("nature_intervention");
            }
        }

        /// <remarks/>
        public string code_projet_TDF {
            get {
                return this.code_projet_TDFField;
            }
            set {
                this.code_projet_TDFField = value;
                this.RaisePropertyChanged("code_projet_TDF");
            }
        }

        /// <remarks/>
        public bool impact_TDF {
            get {
                return this.impact_TDFField;
            }
            set {
                this.impact_TDFField = value;
                this.RaisePropertyChanged("impact_TDF");
            }
        }

        /// <remarks/>
        public bool travaux_dangereux {
            get {
                return this.travaux_dangereuxField;
            }
            set {
                this.travaux_dangereuxField = value;
                this.RaisePropertyChanged("travaux_dangereux");
            }
        }

        /// <remarks/>
        public Demandeur demandeur {
            get {
                return this.demandeurField;
            }
            set {
                this.demandeurField = value;
                this.RaisePropertyChanged("demandeur");
            }
        }

        /// <remarks/>
        public IntervenantV2[] intervenants {
            get {
                return this.intervenantsField;
            }
            set {
                this.intervenantsField = value;
                this.RaisePropertyChanged("intervenants");
            }
        }

        /// <remarks/>
        public string num_di {
            get {
                return this.num_diField;
            }
            set {
                this.num_diField = value;
                this.RaisePropertyChanged("num_di");
            }
        }

        /// <remarks/>
        public string num_bt {
            get {
                return this.num_btField;
            }
            set {
                this.num_btField = value;
                this.RaisePropertyChanged("num_bt");
            }
        }

        public event System.ComponentModel.PropertyChangedEventHandler PropertyChanged;

        protected void RaisePropertyChanged(string propertyName) {
            System.ComponentModel.PropertyChangedEventHandler propertyChanged = this.PropertyChanged;
            if ((propertyChanged != null)) {
                propertyChanged(this, new System.ComponentModel.PropertyChangedEventArgs(propertyName));
            }
        }
    }


    /// <remarks/>
    [System.CodeDom.Compiler.GeneratedCodeAttribute("System.Xml", "4.0.30319.34230")]
    [System.SerializableAttribute()]
    [System.Diagnostics.DebuggerStepThroughAttribute()]
    [System.ComponentModel.DesignerCategoryAttribute("code")]
    [System.Xml.Serialization.SoapTypeAttribute(Namespace="http://mysite/acces_net")]
    public partial class ResultatReqDa : object, System.ComponentModel.INotifyPropertyChanged {

        private string nb_demandesField;

        private Demande[] demandesField;

        /// <remarks/>
        [System.Xml.Serialization.SoapElementAttribute(DataType="integer")]
        public string nb_demandes {
            get {
                return this.nb_demandesField;
            }
            set {
                this.nb_demandesField = value;
                this.RaisePropertyChanged("nb_demandes");
            }
        }

        /// <remarks/>
        public Demande[] demandes {
            get {
                return this.demandesField;
            }
            set {
                this.demandesField = value;
                this.RaisePropertyChanged("demandes");
            }
        }

        public event System.ComponentModel.PropertyChangedEventHandler PropertyChanged;

        protected void RaisePropertyChanged(string propertyName) {
            System.ComponentModel.PropertyChangedEventHandler propertyChanged = this.PropertyChanged;
            if ((propertyChanged != null)) {
                propertyChanged(this, new System.ComponentModel.PropertyChangedEventArgs(propertyName));
            }
        }
    }

    [System.CodeDom.Compiler.GeneratedCodeAttribute("System.ServiceModel", "4.0.0.0")]
    public interface AccesNetWsdlPortTypeChannel : TDF.OSSExtranet.BusinessProxies.ServiceReference1.AccesNetWsdlPortType, System.ServiceModel.IClientChannel {
    }

    [System.Diagnostics.DebuggerStepThroughAttribute()]
    [System.CodeDom.Compiler.GeneratedCodeAttribute("System.ServiceModel", "4.0.0.0")]
    public partial class AccesNetWsdlPortTypeClient : System.ServiceModel.ClientBase<TDF.OSSExtranet.BusinessProxies.ServiceReference1.AccesNetWsdlPortType>, TDF.OSSExtranet.BusinessProxies.ServiceReference1.AccesNetWsdlPortType {

        public AccesNetWsdlPortTypeClient() {
        }

        public AccesNetWsdlPortTypeClient(string endpointConfigurationName) : 
                base(endpointConfigurationName) {
        }

        public AccesNetWsdlPortTypeClient(string endpointConfigurationName, string remoteAddress) : 
                base(endpointConfigurationName, remoteAddress) {
        }

        public AccesNetWsdlPortTypeClient(string endpointConfigurationName, System.ServiceModel.EndpointAddress remoteAddress) : 
                base(endpointConfigurationName, remoteAddress) {
        }

        public AccesNetWsdlPortTypeClient(System.ServiceModel.Channels.Binding binding, System.ServiceModel.EndpointAddress remoteAddress) : 
                base(binding, remoteAddress) {
        }

        public TDF.OSSExtranet.BusinessProxies.ServiceReference1.ResultatReqDa listeDemandeAcces(string login, string password, TDF.OSSExtranet.BusinessProxies.ServiceReference1.RequestDAFilter filter) {
            return base.Channel.listeDemandeAcces(login, password, filter);
        }
    }

}

And here is the response from the service :

HTTP/1.1 200 OK
Date: Thu, 29 Oct 2015 11:01:17 GMT
Server: Apache
X-SOAP-Server: NuSOAP/0.7.2 (1.94)
Content-Length: 17798
Keep-Alive: timeout=15, max=100
Connection: Keep-Alive
Content-Type: text/xml; charset=UTF-8

<?xml version="1.0" encoding="UTF-8"?><SOAP-ENV:Envelope SOAP-ENV:encodingStyle="http://ift.tt/wEYywg" xmlns:SOAP-ENV="http://ift.tt/sVJIaE" xmlns:xsd="http://ift.tt/tphNwY" xmlns:xsi="http://ift.tt/ra1lAU" xmlns:SOAP-ENC="http://ift.tt/wEYywg" xmlns:tns="http://ift.tt/1MkRD6P">
<SOAP-ENV:Body><ns1:listeDemandeAccesResponse xmlns:ns1="http://mysite/acces_net"><resultat_req_da xsi:type="tns:ResultatReqDa">
<nb_demandes xsi:type="xsd:integer">10</nb_demandes>
<demandes xsi:type="SOAP-ENC:Array" SOAP-ENC:arrayType="tns:demande[10]">
<demande xsi:type="tns:Demande">
    <num_demande xsi:type="xsd:integer">579</num_demande>
    <date_demande xsi:type="xsd:dateTime">2012-02-15T16:13:27.181509+01:00</date_demande>
    <statut_dem_acces xsi:type="xsd:integer">1</statut_dem_acces>
    <code_site xsi:type="xsd:string">T59067</code_site>
    <code_ig xsi:type="xsd:string">3530703</code_ig>
    <zone_intervention xsi:type="tns:ZoneIntervention">
        <local xsi:type="xsd:boolean">false</local>
    </zone_intervention>
    <date_deb_intervention xsi:type="xsd:dateTime">2012-02-29T09:00:00+01:00</date_deb_intervention>
    <date_fin_intervention xsi:type="xsd:dateTime">2012-02-29T11:00:00+01:00</date_fin_intervention>
    <accompagnement_demande xsi:type="xsd:boolean">true</accompagnement_demande>
    <accompagnement_requis xsi:type="xsd:boolean">true</accompagnement_requis>
    <nature_intervention xsi:type="xsd:integer">0</nature_intervention>
    <code_projet_TDF xsi:type="xsd:string"></code_projet_TDF>
    <travaux_dangereux xsi:type="xsd:boolean">false</travaux_dangereux>
    <demandeur xsi:type="tns:Demandeur">
        <nom xsi:type="xsd:string">Legoff</nom>
        <prenom xsi:type="xsd:string">Yvon</prenom>
        <telephone xsi:type="xsd:string">0612345678</telephone>
        <email xsi:type="xsd:string"></email>
    </demandeur>
    <intervenants xsi:type="SOAP-ENC:Array" SOAP-ENC:arrayType="tns:IntervenantV2[1]">
        <intervenant xsi:type="tns:IntervenantV2">
            <inter_soc xsi:type="xsd:string">TDF</inter_soc>
            <inter_nom xsi:type="xsd:string">Legoff</inter_nom>
            <inter_prenom xsi:type="xsd:string">Yvon</inter_prenom>
            <inter_tel1 xsi:type="xsd:string">0612345678</inter_tel1>
            <inter_email xsi:type="xsd:string"></inter_email>
        </intervenant>
    </intervenants>
    <num_di xsi:type="xsd:string">992625</num_di>
</demande>
</demandes>
</resultat_req_da>
</ns1:listeDemandeAccesResponse></SOAP-ENV:Body></SOAP-ENV:Envelope>

If someone could help me figure out why the system can't deserialize the data, it would be nice :) .

Thank you in advance.