[otrs] OTRS 3.1: change free fields content from ticket detail

Hi all, When I select to view a ticket's detail and try to press free field from the ticket detail menu otrs generates a popup with the following error description "An error occured! Do you want to see the complete error message?" If I select yes the description is the one in the attached picture. Could this behavior be a bug or it is an upgrade error ? Thank you in advance MV