This message "Selector: can't mint new with no subform." appears in the UI of forms which used to wok.
The subform does not have to be set directly, it can be found by setting "from class" and then that class having a creation form.
The code complains is a Choice has no subform, but although it is useful to have one, it is not essential, as a subform canbe found from the class of the thing to be created, wand that class is always provided.
This message "Selector: can't mint new with no subform." appears in the UI of forms which used to wok. The subform does not have to be set directly, it can be found by setting "from class" and then that class having a creation form.