To resolve, please try the following:
  1. Navigate to Communities > Special Events > Friends Asking Friends > Kintera Thon
  2. Hover over the event name and click Website Info
  3. Beneath Required Items, click on Event Text
  4. Under the first section, Event Definitions, scroll down until you see the first "Save" button on the page
  5. Hit Save
  6. Navigate back to the Webinfo Checklist
  7. Update Your Event Now
This may refresh the settings of the registration page and resolve the error that was previously appearing.
If the problem persists, Contact Support and reference this article.