mono client.exe 

Unhandled Exception: System.Web.Services.Protocols.SoapException: Object reference not set to an instance of an object
  at System.Web.Services.Protocols.SoapHttpClientProtocol.ReceiveResponse (System.Net.WebResponse response, System.Web.Services.Protocols.SoapClientMessage message, System.Web.Services.Protocols.SoapExtension[] extensions) [0x00000] 
  at System.Web.Services.Protocols.SoapHttpClientProtocol.Invoke (System.String method_name, System.Object[] parameters) [0x00000] 
  at Server.Send (System.String user, System.String password, .Message[] messages) [0x00000] 
  at (wrapper remoting-invoke-with-check) Server:Send (string,string,Message[])
  at SMS.Client.Main (System.String[] args) [0x00000]