I was experiencing this exact issue today. I saw a lot of suggestions to delete /tmp/.X11-unix, but when I tried that I found that it was mounted as read-only. This is what I did to resolve the issue:
kill kex
sudo su
mount -o remount rw /tmp/.X11-unix
exit
cd ~
start kex
kex
That resolved the issue for me (without having to actually delete the /tmp/.X11-unix directory).