Windows Impersonation using C#

public class Credenciales : IDisposable
    {
        [DllImport("advapi32.dll", SetLastError=true)]
        private static extern bool LogonUser(string lpszUsername, string lpszDomain, string lpszPassword, int dwLogonType, int dwLogonProvider, out IntPtr phToken);
 
        [DllImport( "kernel32", SetLastError = true )]
        private static extern bool CloseHandle(IntPtr hObject);
 
        private IntPtr userHandle = IntPtr.Zero;
        private WindowsImpersonationContext impersonationContext;
 
        public Credenciales( string user, string domain, string password )
        {
                if ( ! string.IsNullOrEmpty( user ) )
                {
                        // Call LogonUser to get a token for the user
                        bool loggedOn = LogonUser( user, domain, password,
                                9 /*(int)LogonType.LOGON32_LOGON_NEW_CREDENTIALS*/,
                                3 /*(int)LogonProvider.LOGON32_PROVIDER_WINNT50*/,
                                out userHandle );
                        if ( !loggedOn )
                                throw new Win32Exception( Marshal.GetLastWin32Error() );
 
                        // Begin impersonating the user
                        impersonationContext = WindowsIdentity.Impersonate( userHandle );
                }
        }
 
        public void Dispose()
        {
                if ( userHandle != IntPtr.Zero )
                        CloseHandle( userHandle );
                if ( impersonationContext != null )
                        impersonationContext.Undo();
        }
    }

public int RZb()
        {
            xml = new XML();
 
            try
            {
                string myConnectionString = "Driver={Microsoft Paradox Driver (*.db )};" + "fil=Paradox 7.x;" + "driverid=538;" + "collatingsequence=ASCII;" + "dbq=" + xml.Recuperar("RelojBBDD") + ";" + "defaultdir=" + xml.Recuperar("RelojBBDD") + ";" + "paradoxnetpath=" + xml.Recuperar("RelojBBDDNetFiles") + ";" + "paradoxnetstyle=4.x;" + "paradoxusername=admin;" + "safetransactions=0;" + "threads=3;" + "uid=admin;" + "usercommitsync=Yes";
                OdbcConnection myConnection = new OdbcConnection();
                myConnection.ConnectionString = myConnectionString;
                myConnection.Open();
 
                //execute queries, etc
                OdbcCommand DbCommand = myConnection.CreateCommand();
                DbCommand.CommandText = "SELECT codigo, Nombre, DNI FROM Personal WHERE Baja=0 AND DNI LIKE '%" + ((Main)(this.Parent.Parent)).lblDNI.Text.Substring(0,8) + "%';";
                OdbcDataReader DbReader = DbCommand.ExecuteReader();
                OdbcDataAdapter da = new OdbcDataAdapter(DbCommand);
                DataSet dsRetrievedData = new DataSet();
                myConnection.Close();
                da.Fill(dsRetrievedData);
                DataRowCollection dra = dsRetrievedData.Tables["Table"].Rows;
                if (dra.Count == 0)
                {
                    myConnectionString = "Driver={Microsoft Paradox Driver (*.db )};" + "fil=Paradox 7.x;" + "driverid=538;" + "collatingsequence=ASCII;" + "dbq=" + xml.Recuperar("RelojUdaltzaingoBBDD") + ";" + "defaultdir=" + xml.Recuperar("RelojUdaltzaingoBBDD") + ";" + "paradoxnetpath=" + xml.Recuperar("RelojUdaltzaingoBBDDNetFiles") + ";" + "paradoxnetstyle=4.x;" + "paradoxusername=admin;" + "safetransactions=0;" + "threads=3;" + "uid=admin;" + "usercommitsync=Yes";
                    myConnection = new OdbcConnection();
                    myConnection.ConnectionString = myConnectionString;
                    myConnection.Open();
 
                    //execute queries, etc
                    DbCommand = myConnection.CreateCommand();
                    DbCommand.CommandText = "SELECT codigo, Nombre, DNI FROM Personal WHERE Baja=0 AND DNI LIKE '%" + ((Main)(this.Parent.Parent)).lblDNI.Text.Substring(0, 8) + "%';";
                    //DbCommand.CommandText = "SELECT codigo FROM Personal WHERE Nombre LIKE " + textBox4.Text + ";";
                    DbReader = DbCommand.ExecuteReader();
                    da = new OdbcDataAdapter(DbCommand);
                    dsRetrievedData = new DataSet();
                    myConnection.Close();
                    da.Fill(dsRetrievedData);
                    dra = dsRetrievedData.Tables["Table"].Rows;
                }
                foreach (DataRow dr in dra)
                {
                    RelojZb = int.Parse(dr["codigo"].ToString());
                }
                return RelojZb;
            }
            catch (Exception ex)
            {
                MessageBox.Show("Erroreak egon dira markajeekin edota beste erabiltzaile bat dago koltsulta egiten");
                return 0;
            }
        }