Well, I hadn't seen rtra's post before trying KaYoS' suggestion. And it worked. But I was a little confused as to why it worked. rtra's post cleared that up
Also now that I've got it working, I've remembered that I've never been able to get a separate /boot partition on Slack to work properly. I used to use it when I ran RedHat (way back with RH8).
And if it wasn't for this problem, I would still be an unregistered user as well
Thanks to you both.