If you're having trouble logging in, try using the "forgot password" link on the login page at tandemperform.com. This will prompt you to enter a valid email address and then TandemPerform will send you an email with a new link to reset your password.
Once you have set your password using the link to this screen, the link will be invalidated. If you try to use an old link to access the screen, you'll receive an error that says "the fields don't match." For security reasons, this is a one use link.