I am signing in on another machine and it is telling me to "Release All Licenses". What does this mean?

It seems you have licensed your plugins on another machine. By pressing the "Release All Licenses" button it will remove the licenses from the machine that the licenses are on so that you can then use them on your current machine. After pressing the button, it will remove all the licenses, then proceed to get licenses for you for the machine you are on.

If you were then to go back to your previous machine and run Cinema 4D, it will automatically sign you out of that machine. All the licenses will be removed and the plugins will no longer work. You will then have to press the "Release All Licenses" button on this machine, or alternatively you could go to the machine with the licenses and press "Sign Out and Release License".