Compositing with Natron

Hi everyone ! This is my very first post here and since I am new, I hope my question is not yet answered in another topic…
I will learn how the compositing process work tomorrow, for an intense 3-days course, working with Natron. I have a scene ready to work with in Blender, and I rendered it un png.
My problem is that I want to render it in an open EXR Multilayer, to be able to interact separately on my diffuse, ao, color & co passes in Natron. All the passes I need are checked in my blend file, but when I render it in EXR, it shows as a full black image with no layers… Do you have an idea on how can I fix it ? I’m pretty sure the cause of my problem is something infinite and ridiculous, but I am not skilled enough to find an answer by myself, and I didn’t managed to find it on the net…
Thanks !!

I had some issues with earlier versions of Blender where rendering to multilayer exr had distorted and incorrect information on layers.
2.77 seems to work fine.
http://img.ctrlv.in/img/16/03/28/56f9902e52fa5.png

As a suggestion - leave connected Composite output node on render.

I will check it on the new version then, and leave connected the composite node, thanks a lot !