Hi Jason, thanks for helping.
It seems that it was really a memory limit issue. Now the page uploads/updates correctly the images.
I removed the redirect urls, but for my purpose I need them so I'll try to rewrite and see what happens.
It's not the first time I use file upload and it has never happened anything like this.
If this trouble should happen again, how can I check if the problem is memory limit ?
Thanks for now.