The Full Meeting to Organizers popup informs the presenter that people can't log in, which isn't something the presenter can do anything about at that time. And it's in the middle of the screen, even when the gotomeeting window is minimized, which is pretty annoying, especially because it come up every time an attempt to join is made.
Have it show then the gotomeeting window is showing, if you have to, but not when minimized. Instead of the Full Meeting message, have a post-meeting summary where it notes that X people tried to joing and couldn't because of the subscriptions size.
I've changed this to an Idea so it can be considered for a future update. When the message first appears you should see a "do not show this again" option that will disable it for the rest of that meeting.