As an anti-spambot measure, new accounts need to be verified before they can fully participate in the site. After signing up, users should receive an e-mail at the address they signed up with. Clicking a link in that e-mail (or copy-pasting the URL to the browser) will verify their account. Some users' email services block The Duck verification e-mail thinking it's spam.
If you do not receive the verification e-mail, you can either:
The forum thread has a better chance to be addressed sooner, since both admins can see it. The admins can't be on the site 24/7 so it can take up to a day to get it fixed.