I updated to IE 6.something, still getting many problems and it was driving me crazy!!! After days and days, so I emailed ual last night.

"Dear Valued Customer,

Thank you for your inquiry. We are working to resolve a clerical
error that caused this security certificate to be revoked. There is no
security issue with the site, and United Airlines bears no fault in the
error message that is being displayed. The security of our website is of
paramount importance to united.com, and we are working vigorously to
correct this unfortunate mistake.

Sincerely,
Amy
United Web Support "


So far today it works!!!!!!!!!
Could it be.... yes, someone did it . Thanks UAL!