can't access this site

I can't seem to access the site below via my proxy.

http://www.insidecoair.com/flightoperations

But when I try a direct connect (bypassing the proxy) I can readily connect to
it. Can someone please tell me what's wrong? The above has been defined as:

acl air url_regex insidecoair\.com/flightoperations
http_access allow air
http_access deny allow

The site actually is restricted but then it should give you a window asking for
a login.

Thanks,
Joel