When new users are invited to Aha, they are sent a link that directs them to the login page. It's not immediately obvious what to do. The link on this page says "I need to create my password". A lot of people miss this link. I've gotten this question multiple times since we started inviting users.
The link that is in the email sent to new users is directly to the page to create their password. The "I need to create my password" link is only for people who do not use the link in the email they were sent.