Problems with Mailkit IMAP - Authentication with string is not possible

Question

I have a strange problem with my IMAP authentication here. I cannot authenticate if I´m trying to use string variables. I really need to type in my account and my password which does really make no sense to me.

THIS DOES NOT WORK!

    using (var client = new ImapClient(new ProtocolLogger("imap.log")))
        {

            using (var cancel = new CancellationTokenSource())
            {
                //LogIn
                client.Connect("imap.gmail.com", 993, MailKit.Security.SecureSocketOptions.SslOnConnect);
                var credentials = new NetworkCredential(username, password);
                client.Authenticate(credentials, cancel.Token);


                var personal = client.GetFolder(client.PersonalNamespaces[0]);
                f1.tbl_folderTableAdapter1.Insert(ID, PARENTID, username);

                client.Disconnect(true);
            }
        }

BUT THIS WORK

  using (var client = new ImapClient(new ProtocolLogger("imap.log")))
        {

            using (var cancel = new CancellationTokenSource())
            {
                //LogIn
                client.Connect("imap.gmail.com", 993, MailKit.Security.SecureSocketOptions.SslOnConnect);
                client.Authenticate("funnyemailhere", "anothernicepasswordhere");


                var personal = client.GetFolder(client.PersonalNamespaces[0]);
                f1.tbl_folderTableAdapter1.Insert(ID, PARENTID, username);

                client.Disconnect(true);
            }
        }

Can you see any problems here ?

Thank you in advance