I installed v2.0.15 and initially it looked like the install was 100% successful, but when I went to make a change to one of the settings I got dropped out of the backend with the "Forbidden - You don't have permission to access on this server" message, I re-installed v2.0.15 and now like Yann Anderson I can't go pass Step 5 and am seeing the same screen.
I was able to exit and finish the update using the Maintenance and Migrators options in the backend, everything works ok in the easysocial menus, except the settings menu ... if I try and change then save anything in there I get dropped out of the backend with the "Forbidden" message.
This would be a problem, but it turns out the Import and Export buttons still work so I was able to export out my settings make a change to the setting I'd been trying to change and then import the settings back in.
One final thing I tried changing one of the administrator accounts so it could make changes to the ES settings menu, but the same thing happens to that account as well.
Sorry I can't give you access to my site