United Airlines Reservatioin web page error.

Our Company is having issues using the United Airlines (http://www.united.com) web site to make reservations.  After typing in the fligh criteria the site does a search and should return a screen with available flights but instead returns and error page from United saying the request could not be processed.   United claims they are not having any issues and I have confirmed that the site works fine when I connect using AT&T as the IP provieder.   Could there be a DNS issue or some other reson the site doesn't work using Comcast?