Fixer Theme Gives Error When Saving

I am using the Upfront/Fixer theme for the first time and am experiencing a huge issue. Every time I try to save my changes to the theme components, I get a save error. It simply says "There has been an error saving your changes" and offers no other information.

This is a brand new WordPress installation with only the theme and the Appointments WPMU plugin installed, plus the default WordPress stuff. Pretty permalinks is activated. What am I doing wrong?