The remote certificate is invalid according to the validation procedure. I have given the consumerkey and consumersecret in Start.Auth.cs.
see the servicepointmanager.servercertificatevalidationcallback documentation
Setting the callback overrides the default behaviour and you can yourself create a custom validation routine.
ServicePointManager.ServerCertificateValidationCallback += (sender, certificate, chain, sslPolicyErrors) => { return true; };
Obviously you have to attach the callback before performing the login :-)