Speak the user’s language

This screenshot comes from a web site where I’m registered and where I’ve bought items in the past. What do you think I did wrong?

Pic001

It turns out I entered a different e-mail address to the one I used to register at this site. But I’m not sure how I was meant to divine that from this error message.

The Post Office shows how not to do it

I ordered some foreign currency from the Post Office today. I was a bit disappointed by needing to opt-in to opt-out of spam:

Pic002

I was then disappointed some more when I was asked to press the ‘Purchase Order’ button, but my only choices were ‘Buy Now’ and ‘Cancel Order’. I know it’s not hard to work out the right choice, but this is totally unacceptable in a user interface.
Pic001
Incidentally, after clicking on the Buy Now button I went through a ‘Verified By Visa’ section. Maybe I entered my password wrongly, but when I was returned to the Post Office screen I was told that the transaction had failed and I needed to start again. 

Which of these two options do you think is the correct one?

(a) It had remembered all my address details so I didn’t need to enter them again.
(b) I had to type it all again.

Based on the site’s previous performance, you don’t really need me to tell you the answer, do you?