Can't activate nor deactivate any administrator permissions outside of safe mode
If you are using an app such as Facebook Messenger, CF.lumen, Lux or Twilight that draws over the screen, you'll need to stop them doing so in order to interact with secure settings pages such as the device administrator activation/deactivation pages.

For example, in Facebook Messenger, you would either close all chat heads or go to the Facebook Messenger settings and deselect 'Chat Heads', or in CF.lumen you would disable the overlay by pressing 'Disable' in the persistent notification.