Hi Ludo. I'm having this same problem, but in Mac OSX.
I copied the MGLToolsPckgs to that same directory. I also installed upy_addons.zip.
Just to be one the safe side, I also copied MGLToolsPckgs to my blender plugins directory: /Users/{USERNAME}/Library/Application Support/Blender/2.79/scripts/addons/
That didn't fix the error. Thanks.