ES File Explorer Pro: root access error on Android 6
I found a solution:


Install Busybox and Android Terminal Emulator.
Open the terminal app and write these commands "enter" separated: su, mount -o remount,rw /system, touch /sbin/su /system/bin/su /system/xbin/su, mount -o remount,ro /system, exit.
Reboot


Now you can enable the Root Explorer feature in ES File Explorer without any error!