Get MAC IP for use in indicator

I input these code:

public string GetMACAddress()
        {
            NetworkInterface[] nics = NetworkInterface.GetAllNetworkInterfaces();
            string sMacAddress = "";
            try
            {
                foreach (NetworkInterface adapter in nics)
                {
                    // only return MAC Address from first card  
                    if (sMacAddress == String.Empty)
                    {
                        IPInterfaceProperties properties = adapter.GetIPProperties();
                        sMacAddress = adapter.GetPhysicalAddress().ToString();
                    }
                }
            } catch
            {
                sMacAddress = "";
            }
            return sMacAddress;
        }

How can I solve these Errors.

Thank you.