Server error 500 when activating the plugin

Hi I get an Server error 500 everytime I try to activate the plugin. I have to delete the folder and my site is back right away. I got to activate it the first time but when I clicked on “Start up” to install the page the site got 500. Since then I got to deleted those pages, delete the usersultra databases, repaired and optimized the other databases but nothing works, I always have the same error message. Using php 5.6
Thank you

https://wordpress.org/plugins/users-ultra/