Need a c# code for device configuration

[Deepak]

when i used SetNetworkInterfaces() method of deviceio.wsdl web service and NetworkInterfaceSetConfiguration ,there is an error of object reference not set

                                networkInterfaceSetConfiguration.Enabled = true;
                                //enable this new configuration
                                networkInterfaceSetConfiguration.IPv4.Enabled = true;
                                //enable it to be IPv4
                                             networkInterfaceSetConfiguration.IPv4.Manual[0].Address="192.168.1.20";
                                //ip address
                                networkInterfaceSetConfiguration.IPv4.Manual[0].PrefixLength =24;
                                //netmask
                               networkInterfaceSetConfiguration.IPv4.DHCP =false;