First try another one, but it can happen that all machines of a station are "fuori servizi" don't work. During all February 2008 the six machines at the urban railway station Gemelli (deserving the major Roman hospital) were out of service!
What to do? Don't think it is not your problem. On your ticket is written, only in Italian, in very small characters, that you have to validate your ticket by writing on it datum, time, station "In caso di malfunzionamento dell'obliteratrice il viaggiatore dovra annulare il titolo di viaggio apponendovi la data, l'ora ed il numero di vettura o la stazione sul retro".
Do that, at Gemelli station (urban train line FM3) I had just hand filled in my BIT ticket that there was a control on the train.
Another thing; when validating your ticket in a machine turn the illustrated side down. The machine prints on the upper side.

