Just a quick comment. are you sure the server has permissions to that file? You problem looks very much like a permission problem.
I usually set the group to www-data (the server) and grant full rights to owner and group
Code:
sudo chgrp -R www-data <folder name>
sudo chmod -R 774 <folder name>
Just be ware: '-R' means recursive, that is rights are ganted to all subfolders and files as well.