Oh, it means not enough? That's... odd. It doesn't mention a team name. What I put in the title is exactly the message I get (without the ? in game, though, of course

). All the teams have 25 on their active roster. Two teams have 7 players on one of their minor league teams - one's a Short A and one's a Rookie league team, but neither league has a min or max players per team limit.
Argh, found the problem. Allow incomplete minor league rosters wasn't ticked when I thought it was. Sorry