just started having the same problem on my punto.took the gearbox out,found the thrust bearing washer had broken and damaged the clutch diaphragm teeth.just putting it all back together at the moment.hope this gives you a clue.
p hunt
November 2007
Have your gearbox oil checked and replaced, Fiat suggests that you replace the gearbox oil every 70,000 miles, this should resolve the problem, with low gearbox oil it can be difficult to change gears as they are not properly lubricated.