I had an annoying one recently at IAH (which, by the way, has a very nice setup of kiosks as you enter the passport area - best I've seen). My wife and I both GE and both cleared by our machines but my printer jammed and no ticket came out at all! There is an agent dedicated to the GE line so I asked if I could redo the entry on a different machine and he said no - have to fill out a manual blue form and have him stamp it, which he did. He seemed to know that that machine's printer was acting up already and from what I could tell he didn't go over to put and OOO sign on it. Not a real big deal but still an annoyance and not clear how customs would have worked if I had wanted to use the GE exit since I had a manual form. Still overall a great program.