After using the News Ticker App for a while, you are no longer able to edit the content of the app. You receive an error message like this : “Correlation ID: ace84e9c-b7b8-905c-fef5-4b737de9240aC”
Sometimes the SharePoint App model has problems with WebParts/AppParts by installing a new Masterpage on the SharePoint Site.
Remove the News Ticker App and re-insert it into the page. Then the content is editable again.