I was told only paying members may download this item, but I've already paid!
You may have created a new account (with a new username), then logged into your old free/expired account by mistake. Try logging in again with the username and password for your NEW account.
If you get the same error message after attempting to log into your paid account, please go to the Find Me page. Here, you can enter your email address and have all Usernames/Passwords associated with that email address sent to you.