Ok, the link is now working, thanks!
Unfortunately, my previous error is still present: now it gives me error not on 0%, but on 56~96% of every upload…
Wanting to try the 2.0.10 beta (the official release seems to give me error while uploading images) but the link for the download seems to be broken.
This is the link: http://www.nextgen-gallery.com/nextgen-gallery-latest-beta/%5Bs2File%20download=%22nextgen-gallery-v2.0.10.zip%22%20download_key=
Is it correct?