The failure shut down United's website for more than two hours and prevented workers from boarding passengers on time. United passengers reported long lines in the airline's hubs in Newark, New Jersey, San Francisco, Houston, and Chicago. It also caused nine cancellations.
United Continental Holdings Incorporated said Wednesday that it's still working to find out why the computer equipment didn't work right.
The problems came on the same day that airlines already had to deal with Hurricane Isaac, which has disrupted travel in cities around the Gulf of Mexico.