Thebox a long shot

it could be your security apps are blocking the site or part of it. i dont recommend you disable any security just to sign up if thats the reason as it may well be doing it for a reason(malware/bad scripts/phising).
compare your security apps with yer m8's if they have the same and are setup the same then you can look at yer provider but its unlikley they are blocking anything if your living in the e.u or u.s.a.