error occured when i call a method in my web service

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[WebMethod]<br />
        public FactureTopNet CreationFacture( ref int NUM_FACTURE, ref  int NUM_JUR_FACT,ref  int SOCIETE, ref int TYPE, ref string LOGIN_CREATION,ref  DateTime DATE_CREATION, ref string LOGIN_MODIFICATION,ref  DateTime DATE_MODIFICATION,ref  Decimal MNT_FACT,ref  decimal REMISE, ref decimal NET_PAYE,ref decimal REST_PAYE,ref  string OBSERV, ref int ID_CLIENT,ref  string REMARQUE,ref  string MONTANTTEXT, ref int TIMBRE, ref int AVOIR, ref int NUM_LISTE,ref  int ID_REV,ref  int NUM_PF, ref int NUM_PP, ref string REFERENCE, ref string CLE, ref int ID_COM,ref  decimal MONTANT_COM, ref DateTime DATE_COM,ref int RED_COM, ref  int INTER_GROUPE)<br />
        {<br />
<br />
            System.Data.OleDb.OleDbConnection conn = new System.Data.OleDb.OleDbConnection();<br />
            conn.ConnectionString = @"Provider=SQLOLEDB.1;Integrated Security=SSPI;Persist Security Info=False;User ID=topnet;Initial Catalog=TopnetBase;Data Source=SWEET-4B6F892B4\SQLEXPRESS";<br />
            conn.Open();<br />
            FactureTopNet facture = new FactureTopNet();<br />
            int r;<br />
            string req = "INSERT INTO facture (NUM_FACTURE, NUM_JUR_FACT, SOCIETE, TYPE, LOGIN_CREATION, DATE_CREATION,LOGIN_MODIFICATION,DATE_MODIFICATION,MNT_FACT, REMISE, NET_PAYE, REST_PAYE, OBSERV, ID_CLIENT, REMARQUE, MONTANTTEXT, TIMBRE, AVOIR,NUM_LISTE,ID_REV,NUM_PF,NUM_PP, REFERENCE, CLE, ID_COM,MONTANT_COM, DATE_COM, RED_COM, INTER_GROUPE)VALUES('" + NUM_FACTURE + "','" + NUM_JUR_FACT + "','" + SOCIETE + "','" + TYPE + "','" + LOGIN_CREATION + "','" +DATE_CREATION + "','" + LOGIN_MODIFICATION + "','" + DATE_MODIFICATION + "','" + MNT_FACT + "','" + REMISE + "','" + NET_PAYE + "','" + REST_PAYE + "','" + OBSERV + "','" + ID_CLIENT + "','" + REMARQUE + "','" + MONTANTTEXT + "','" + TIMBRE + "','" + AVOIR + "','" + NUM_LISTE + "','" + ID_REV + "','" + NUM_PF + "','" + NUM_PP + "','" + REFERENCE + "','" + CLE + "','" + ID_COM + "','" +MONTANT_COM + "','" + DATE_COM + "','" + RED_COM + "','" + INTER_GROUPE + "')";<br />
            System.Data.OleDb.OleDbCommand command = new System.Data.OleDb.OleDbCommand(req, conn);<br />
            r = command.ExecuteNonQuery();<br />
            facture.NUM_FACTURE = NUM_FACTURE;<br />
            facture.NUM_JUR_FACT = NUM_JUR_FACT;<br />
           <br />
            facture.SOCIETE = SOCIETE;<br />
            facture.TYPE = TYPE;<br />
            facture.LOGIN_CREATION = LOGIN_CREATION;<br />
            facture.DATE_CREATION = DATE_CREATION;<br />
            facture.LOGIN_MODIFICATION = LOGIN_MODIFICATION;<br />
            facture.DATE_MODIFICATION = DATE_MODIFICATION;<br />
            facture.MNT_FACT = MNT_FACT;<br />
            facture.REMISE = REMISE;<br />
            facture.NET_PAYE = NET_PAYE;<br />
            facture.REST_PAYE = REST_PAYE;<br />
            facture.OBSERV = OBSERV;<br />
            facture.ID_CLIENT = ID_CLIENT;<br />
            facture.REMARQUE = REMARQUE;<br />
            facture.MONTANTTEXT = MONTANTTEXT;<br />
            facture.TIMBRE = TIMBRE;<br />
            facture.AVOIR = AVOIR;<br />
            facture.NUM_LISTE = NUM_LISTE;<br />
            facture.ID_REV = ID_CLIENT;<br />
            facture.NUM_PF = NUM_PF;<br />
            facture.NUM_PP = NUM_PP;<br />
            facture.REFERENCE = REFERENCE;<br />
            facture.CLE = CLE;<br />
            facture.ID_COM = ID_COM;<br />
            facture.MONTANT_COM = MONTANT_COM;<br />
            facture.DATE_COM = DATE_COM;<br />
            facture.RED_COM = RED_COM;<br />
            facture.INTER_GROUPE = INTER_GROUPE;<br />
            return facture;<br />
            <br />
            <br />
            <br />
<br />
        }<br />