in this post you may find a hint for your problem.
If it could be caused by a mis-configured .htaccess file or a too low configured php memory limit you should have a look at.
I think the “workaround” to edit line 13xx in nc/updater/index.php is not a good advice, because breaking the update when integrity fails has good reasons…
i would have had a look to the mentioned config files from this post.
You haven’t filled in which webserver you use (apache, nginx, etc.) …?