If you look at the attachment below, you'll see there's only 18 players dressed yet the game is telling me there's already 20 dressed and it's not allowing any more players to be selected.
When I first saw the message, I thought it might be a bug in the game. Shortly thereafter, it dawned on me the ECHL only dresses 18 per game (including goaltenders), so there's actually nothing wrong here except the notification through me for a loop. If the pop-up indicated the maximum number of players had already been reached, or mentioned 18 as opposed to 20, I wouldn't have been so easily confused.