I fired up Update Manager and I checked for updates and I get this error:

and I tried
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 531EE72F4C9D234C
but this gave me THESE errors:

and I have no idea how to fix this. I assume the second error is because of my internet connection, but that's an assumption. I think I should try again later and by running the code above I should get this error sorted out right?