Problem when downloading large files using Storage module
I would have preferred to put this into a comment, but I don't have enough rep points yet. :/

First, a few questions: What version of PHP are you using?  Does the same thing happen with small files?  Are you using symlinks?  Do your server logs show anything suspicious?

I am trying to fix a similar problem on one of my sites.  PHP 5.4 works fine, but 5.5 is choking when trying to interact with the file, which happens to be linked into a mounted filesystem.  They are on different versions of Ubuntu as well, so I am currently trying to figure out if it is a Linux kernel bug, a PHP bug, or a PEBKAC error.