Life without Robot Unicorn Attack? D;
Have you tried using a different account?
Have you accepted the latest terms?
Try changing the date to a day ahead, try downloading it then, and switch the day back.
Make sure you have a valid credit card associated with the account, and it hasn't expired yet.
This is what I can think of now. If anything else comes to mind, I'll post.
Is it starting to install before it fails? If so, it could be a problem with storage. Try downloading it and installing it through your computer.