uses IdSSLOpenSSL, IdIOHandler, IdIOHandlerSocket, IdMessage, IdExplicitTLSClientServerBase, IdFTPCommon
....
  idFtp1.Host := 'ххххххххххх';
  idFtp1.Username := 'хххх';
  idFtp1.Password := 'хххххххххх';

  fSSL:= TIdSSLIOHandlerSocketOpenSSL.Create(nil);
  fSSL.SSLOptions.Mode:=sslmClient;
  fSSL.SSLOptions.Method:=sslvSSLv23;
  fSSL.SSLOptions.SSLVersions:=[sslvSSLv3, sslvTLSv1, sslvTLSv1_1, sslvTLSv1_2];
  idFtp1.IOHandler:=fSSL;   // Вот тут происходит ошибка
  idFtp1.UseTLS:=utUseExplicitTLS;
  idFtp1.DataPortProtection:=ftpdpsPrivate;
  idFtp1.Port := 21;
  idFtp1.Connect;
............................