That's just the point - when I get a list of fares with a button to click on the airline that is offering it, I get the message. Ok, fine, stuff happens. But update your system now that you know there are no fares available...
BTW, I do use this and other services as a free info service, however I will occasionally book my fares on Expedia or Travelocity just out of a sense that I have been using their info and I want them to stay in business. It costs me 5-10 bucks, and of course 1,000 MP miles if I don't use UA's krappy site. I'm probably silly doing this; I wonder if anyone else does the same?