Could not load type 'System.Net.Security.SslStream'

Question

I've this simple C# program:

using Npgsql;
public class App {
  public static void Main(string[] args) {
    const string CONNECTION_STRING = "Host=myserver;Username=mylogin;Password=mypass;Database=mydatabase";
    using (var conn = new NpgsqlConnection(CONNECTION_STRING)) {
      conn.Open();
    }
  }
}

and I compile it with mono (mcs):

mcs -target:exe -lib:bin -r:System.Data.dll -r:Npgsql.dll -r:System.dll -r:Mono.Security.dll -out:bin/ssl.exe src/App.cs

when I execute, an error thrown:

Unhandled Exception:
System.TypeLoadException: Could not load type 'System.Net.Security.SslStream' from assembly 'System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.
  at Npgsql.NpgsqlConnector.Open () <0x4155f7f0 + 0x00115> in <filename unknown>:0 
  at Npgsql.NpgsqlConnectorPool.GetPooledConnector (Npgsql.NpgsqlConnection Connection) <0x4155c8d0 + 0x00a4f> in <filename unknown>:0 
[ERROR] FATAL UNHANDLED EXCEPTION: System.TypeLoadException: Could not load type 'System.Net.Security.SslStream' from assembly 'System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.
  at Npgsql.NpgsqlConnector.Open () <0x4155f7f0 + 0x00115> in <filename unknown>:0 
  at Npgsql.NpgsqlConnectorPool.GetPooledConnector (Npgsql.NpgsqlConnection Connection) <0x4155c8d0 + 0x00a4f> in <filename unknown>:0 

My Npgsql.dll version

$ monop2 -r Npgsql.dll 

Assembly Information:
Npgsql
Version=2.2.0.0
Culture=neutral
PublicKeyToken=5d8b90d52f46fda7

My compiler:

$ mcs --version
Mono C# compiler version 4.4.0.0

$ mono --version
Mono JIT compiler version 4.4.0 (Stable 4.4.0.40/f8474c4 Mon Mar 28 12:22:29 UTC 2016)
Copyright (`u`C) 2002-2014 Novell, Inc, Xamarin Inc and Contributors. www.mono-project.com
TLS:           __thread
SIGSEGV:       altstack
Notifications: epoll
Architecture:  amd64
Disabled:      none
Misc:          softdebug 
LLVM:          supported, not enabled.
GC:            sgen

Finally, my environment:

$ uname --all
Linux abe 4.5.0-1-ARCH #1 SMP PREEMPT Tue Mar 15 09:41:03 CET 2016 x86_64 GNU/Linux

Thank you

Answer 1

I have one question - do you have library Mono.Security.dll inside bin folder? If so, please delete it and try again.