This usually happens when the radio button option is selected on a Custom Form and only one item is available to choose from.

To fix this, navigate to:
  1. onMessage > Content > Custom Forms
  2. Click Edit to the right of the form
  3. Edit Form
  4. Click Edit next to the radio button item
  5. Enter in another Value within the Add Value textbox
  6. Click Add
  7. Click Save & Exit

User-added image