The links in new user invitation emails and password reset emails expire after 7 days. If your user is experiencing this issue, simply send a new password reset.
This can be handled one of two ways:
By an Admin - A Provider Admin or Provider User on your account can go into the Users table (found in the blue menu bar across the top of your page), find the user in the list and click the orange "Reset" link to the right.
By the User - The user can always request a password reset email, even if they haven't established their account yet, by going to the login page (www.smarterselect.com/login) and click "Forgot Password". Here they'll enter the email address under which their account is set up.