I currently have two x-executable file on my system after downloading them. Neither of them run when double clicking on them.
The first file is a game, Gunpoint, downloaded from the developer's website. Right clicking the file indicates the right checkbox has been ticked in the permissions tab.
The second file is Popcorn Time. Oddly enough, this worked for me on a previous install of Ubuntu without any problems. I purchased a new SSD recently so went with a fresh install.
I'm running 14.04 LTS.