I just find out that in kali-rolling the secondary Xorg server DISPLAY number is 0 instead of the normal 8
(I find this out by looking in /var/log i have Xorg.0.log instead of the normal Xorg.8.log)
so this might cause (Cannot access secondary GPU - error: [XORG] (EE))error in optirun.

so if you have this error, try changing VirtualDisplay=:8 to VirtualDisplay=:0 in /etc/bumblebee/bumblebee.conf
I hope this can help someone