Could you check if example network applications that come with Qt work fine? And could you check if the problem persists if you change the thread generating numbers to something like this:

Qt Code: 
  1. void genthread::run(){
  2.     QTimer timer;
  3.     timer.setInterval(5);
  4.     connect(&timer, SIGNAL(timeout()), this, SLOT(generateNumbers()));
  5.     timer.start();
  6.     exec();
  7. }
  8. void genthread::generateNumbers(){
  9.     if(stopgen) QThread::exit();
  10.     x = (rand() % 10) - 5.0f;
  11.     y = (rand() % 10) - 5.0f;
  12.     z = (rand() % 5) - 2.5f;
  13.     emit message(tr("sending %1 %2 %3...").arg(QString("%1").arg(x), QString("%1").arg(y), QString("%1").arg(z)));
  14.     emit generated(x, y, z);
  15. }
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BTW. With such construction you can get rid of the thread at all and do everything in one thread. It's possible that it's the threading which causes trouble because you didn't have the event loop running (see QThread::exec() for details).