When the screen comes up asking for your username and password both fields are already filled out although the password will be really long and look incorrect leave it alone just hit okay or submit or whatever the button is down below and you will be taken to the download page. Just don't change a thing, that is if you are already logged in.
I was trying to download an attachment from someones post and it said:
Either you are not registered, downloading is not enabled or your username/password were incorrect.
and i know i put in the right password!