UPDATE : october - 11 - 2016 (updated blendFile with packed files and fbx after doing the export again in a clean install of blender 2.77a) Even if I copy the mesh from 2.78 to 2.77a it makes the same problem once I export from 2.77a... it seems to be something in the data of the object itself... it also happens to all the blender files I use to have with 2.78, notice that I removed all the addons before export.
Oct 11 2016
Oct 10 2016
Please follow our submission template and guidelines and make a complete, valid bug report, with required info, precise description of the issue, precise steps to reproduce it, small and simple .blend and/or other files to do so if needed, etc.
Aug 6 2016
Problem solved, don't trust Wacom when it says to update your drivers even if it ask to uninstall. Do this every time you get an update for your Wacom even if you have multiple Wacom devices: Uninstall manually > download latest drivers from their official web page > install > restart. After that, Blender has pen pressure again. Now I'm happy :D
Jul 22 2016
Almost forgot, here the link to the blenderartists thread: https://blenderartists.org/forum/showthread.php?389380-No-pen-pressure-in-the-last-2-or-3-versions-help