SOLVED. Thank you, Baiju, for your kind reply. I worked on your suggestion but I tried to solve the problem without editing internal file, in order to keep the web interface for new settings. I finally found a trick: on the "Employee" menu, I select the "Department" sub-menu from the left bar. As I get the table with several deparments, I click on the "More" selection menu in the department I want to cancel. From "setting" we have a new page where editing on the deparment is possible. Just select "discard" and, magically, you have the "action" button, where "delete" is eligible to remove the object. It seems to work.

Thanks again, Carlo