Unfixable errors

As part of the Rapid Developer path you need to fix some errors in module 4. I've selected an action, entity and page for the button error, however, the errors will not go away (I am using the web modeler). Even when I delete the buttons entirely the errors are still there. Any idea on how to fix this?   
1 answers

Maybe the error is about the details button? (If you check which element the errors are about?) It seems like the properties for the add button are correct.