It seems to be the McAfee site advisor on my PC. Even when I search for the website in Google it has the red cross against it that takes you to the McAfee warning page. I don't have this problem on my laptop, which doesn't have McAfee.
I've not used McAfee SiteAdvisor, but from the reviews I've read online it often warns against safe sites etc. There maybe a setting to turn it off or add sites to a whitelist so it no longer pops up?