A username and a password is required. Open ratings.php with Sublime or Notepad++ and edit the file with your own values.
Write your own username and password and save the file. Remember to attach it to widget settings. Once attached and the site is uploaded, then you can access your Control Panel with the link above, your new username and password.
I am also having this problem as well. I followed the instructions, editing ratings.php in Sublime, changing absolute path to correct path for website, added the php file, but I am still not able to get to the control panel or submit a review. I have deleted and re-added the php file hoping it would be the fix, but it is still not working. I have also deleted the widget from Adobe Muse and re-installed it, but no success.