I've got a very similar problem as the card I use to make payments for unlimited dial-up has expired (NTL automatically take payments of it).
When I log into my account and goto to part of the site in question and try to up date my card details I get the same error code as your self. I've tried differant cards as well!! The thing is I don't fancy phoning the 0902 number as I bet there is big charges
How you getting on?????????????