Here's a bit of a puzzle which I cannot work out.

I'm having issues with Amazon at the moment. Somehow I ended up with two accounts, both registered with the same email address, I shall call them Account A and Account B.

Account A is the one I normally use, I've had it since about 2005.
Account B only came to light after my mum accidentally managed to order something on it - I think it was via 1-Click ordering, although she'd never logged in and I'd not used her computer for over a year.

However the odd thing is that I can only log into Account A from this computer. I can't log in to Account B at all, even when I have reset the password 30 seconds earlier.
Account B can be accessed from any other computer, but no other computer can access Account A :-?

I've managed to change the email address of Account B to my other email so I can at least keep track of the two accounts (and prove there are two!), but can anyone explain
a) how I managed to get two registered to the same email in the first place, and
b) why I can only access one of them only on this computer, and the other one only on any other computer :-?

There's a puzzle to occupy those of you not at work over Christmas and New Year ;D It's got me stumped!