I installed that theme on a

Megan — Wed, 18 Apr 2018 14:01:08 +0000

I installed that theme on a test site to see what was going on here.

Really, this is not a very good way of implementing a slider. It works for an out of the box theme, but as you found out, it breaks down when you want to extend it. Those are just theme settings which are stored as variables. They aren't meant to be used for content.

It would be better to create a content type for your slides and a view to display them. Then there are many slideshow modules you could use to implement the slider (slick or views slideshow are good options). Copy the CSS classes from the theme implementation to your view to make it look the same.

What did you put in your subtheme? All of the code changes in that subtheme? Something is wrong there. It might just need a cache clear but you're not going to be able to do that if you can't log in. It might also be having an issue if it's trying to redeclare functions from the base theme. Try commenting out any custom PHP in your subtheme and try again.

If you're still having trouble, upload a copy of your subtheme and I'll take a look.