Players from Top 30 in singles and Top 15 in doubles who already played 15 small tournaments are not allowed to queue for tournaments from 250/500 series. If someone who already have on the rank 15 small tournaments played, queue for tournament (from 250 and 500) he/she'll be banned.
In Singles Top 30 is allowed to play only 15 small tournaments.
In Doubles Top 15 is allowed to play only 15 small tournaments.
All other players can play tournaments normally.
Generally, players are automatically informed that they can't queue for tournament because they already played 15 small tournaments. But, sometimes system dosen't reacts.
Thanks,
Sampreas