I've just had a problem, not allowed to access A4A. I got a page up with warning about virus etc. It suggested I switch off the router and switch it on again.
Remedy: I went into the control page of the router, disconnected BB then reconnected it and everything was fine (it changed the IP address). I use many websites but this is the only one which objected to the address (the router has been connected for weeks and has been into A4A before). Silly damned thing, but at least I shall know what to do in future.