All of a sudden I get an error 255 without changing anything

I'm building a simple desktop application for a school project. I'm using Qt creator. So I was doing some stuff, it was all going ok, while all of a sudden the application started crashing while giving me error 255.

So when I execute the program, you are in the main window, you select a widget in the list on the left, you click "Modifica Pubblicazione", then on the right appears a widget whose purpose is to edit the publication selected on the list. So here you can edit the infos and click "Conferma" to confirm the changes.

All that was going good until something that I don't know happened. Now when you click on "Conferma" the app crashes and sometimes it gives me an "error 255".

The problem is probably into "view_articles.cpp" and "view_publications.cpp" files, even if I have no idea what is wrong since all was working good until yesterday.

I've uploaded the code on this link: http://ift.tt/2tn8Jnm