cmd up wont work in emacs

I am using Emacs as well as Racket on a Macbook Pro. Both applications rely on Command-UP in order to retrieve the last command in the buffer. This however does nothing. It's obviously an OS-level problem because it happens in both applications. Command-Plus, however, and various other combinations, do work.

This thread in stackoverflow suggested a solution but it didn't work.

https://emacs.stackexchange.com/questions/21285/set-mark-command-c-spc-not-recognised-broken/21311

I need this to work right away. This is very frustrating, hardly the first time my mac has malfunctioned as of late.