This error can appear after copying a page in NetCommunity that previously had an Event Registration Form on that page. Also, this behavior can occur when changing the page template to use a completely different template. When performing this action, the event form will still exist on the page and can allow users to apply another Event Registration Form as a result. In either case, this can cause the page to cache or retain a value that would have the editor see that there is a conflict. To resolve, perform the following: 
  1. In NetCommunity: Navigate to Site Explorer>Pages & Template
  2. Search for the page in question - Does it contain an Event Registration Form?
  3. Search for the template in question - Does it contain an Event Registration Form?
  4. The total number of Event Registration Forms between the Page and Template must only be 1. If there is more than 1, cut the part from the page or template by clicking the Scissors icon next to the part while under Site Explorer>Pages & Templates