If after creating a new account you receive an error when clicking the link in our account validation email, you either have already confirmed your account or the link is no longer valid (validation links expire if unused after a period of time).
If you successfully validated your email, you would have received a confirmation email from Haste.
One way to confirm whether your account is valid is install Haste and enter your credentials.
You can recover your username (at https://haste.net/account-help/?hm=forgot-username) and/or password (https://haste.net/account-help/?hm=forgot-password).
If all else fails, you can recreate your account at https://haste.net/apply-for-beta.