I have a Xamarin app up on the app store. I hadn't touched it for about a year and needed to make a minor update. Of course, OSX wanted me to updated everything, so I updated the OS to latest, updated Xcode to latest, and now my app doesn't build.
Because Xamarin abstracts everything away (good!), I've never had to actually learn to do development on a Mac (bad!), so I don't even know where to start with this error.
I've attached the full error. Can anyone take a look and give me a hint of what direction I should be looking?