It is working now, because it seemed to be a problem with the old temp folder.
I created a new temp folder because into the old one, there were several .part and .part.met files which, in fact, don't exist but they are there into the HD, so when aMule tried to overwrite this kind of "ghost" empty-files, I got that error.
Now with the new temp folder, everything's working right.
Thank you very much.
