Thanks everybody!

No, Mac, it wasn't the hard disk: defragged, but the problem was still there.

And, yes, Rachel, the suggestion you gave on another similar thread, try to record audio to see if the rendering was good or not, is very useful.

But I think that probably the problem is when you choose a number of beats different by the suggested one: I mean, in my case the real tracks style suggestion beat number was 85, but the song was slower (70).

And if I set the beat number to 85 (the style-suggested one) the problem wasn't anymore! Everything in perfect timing in the rendered wav file.

My personal solution: I choose a different style with a "closer" beat number (65), someway similar to the one I had chosen before, then I've changed two tracks (bass and drums) with the ones I preferred from the "old style" and...problem solved!

Ciao a tutti!

http://soundcloud.com/alfredo-de-pietra