It probably wants to drop a heap of tracking cookies on your PC and your firewall is preventing this. I also have NTL 600k BB but not registered for BB Plus. Not at £3-99 per month extra. Here use the
Ontrack Firewall not Norton so unfamiliar with the options the latter gives you. However - I would not disable it. It will have an option to allow you to adjust the settings for some websites to allow these cookies to be landed on you. Personally I always click on "Block cookie" when my firewall puts up the window on a website. Choice is yours.