OK. I solved this problem and now I get an other error. What you need to do is this:
client.Authentication.SslServerTrustHandlers += new EventHandler<SharpSvn.Security.SvnSslServerTrustEventArgs>(Authentication_SslServerTrustHandlers);
void Authentication_SslServerTrustHandlers(object sender, SharpSvn.Security.SvnSslServerTrustEventArgs e)
{
// Look at the rest of the arguments of E, whether you wish to accept
// If accept:
e.AcceptedFailures = e.Failures;
e.Save = true; // Save acceptance to authentication store
}