Just had to run one of the cats to the vets

[Ian Mason]

We've just had to run one the cats to the vets.

What, I hear you asking, has this to do with ukcrypto? Well, the chip &
pin machine at the vets refused our card. "Don't worry", said Natalie  
the receptionist,
"it's always doing that. As long as it isn't because there really is  
a problem with
the account we can just run it again and it'll go through." We did  
and it did.

Now I'm curious and I don't want to wade through thousands of pages  
of EMV to satisfy
my curiosity when there's likely someone better informed on EMV that  
me here. Why did we
get "refused" when clearly the problem was something else. Is this  
just a very poor
error message - where you get "refused" for any failure rather than a  
more helpful
diagnostic such as "transmission error". Or is there a flaw in the  
authentication or
authorisation process that generates a 'real' false negative?