Messages app showing as restricted on school Macbook

For months, my messages app on my Macbook was working completely fine. Suddenly, this message kept popping up and it continued showing up after I quit the application, restarted my computer, and it still shows whenever I try to open Messages. Could this be because I'm on a school Macbook and they enabled a setting suddenly. If anyone knows how to fix this, please tell me.

[Edited by Moderator]

Original Title: Messages Restricted Message