Getting this message when there are 24 players on AvD maps like Dustbowl or Osaka. Perhaps in a way this is a good thing, because with more players it can be difficult to get past choke points.
The work-around to my knowledge is shortening the MOTD so it's under 1KB. If this means that not all rules fit in, you can for example use a rules plugin which displays them via HUD, e.g. when spawning the first time. Though not sure how much text fits on the HUD.
Another work-around would be to limit Battlezone to 24 players, but I suppose that Bz is meant to have 32 players.
Edit: Happens on "well" as well. Probably a lot more maps, feel free to add to the list.
2fort
dustbowl
osaka
well