Hi Please explain why i can enter certain tournaments and on others i get a message: "You are already entered in '1' tournaments.

You can join an unlimited amount of Chess.com official tournaments, but only one tournament created by a member. You have to wait for that tournament to be over to join another.

Basic members can play on only one member-created tournament at a time.

Once all your games in the tournament are over, even if between rounds of a multi-round tournament you may register in another member-created tournament.

Once allowed to register while between rounds of the first tournament, you can play in more than one member-created tournament.

http://www.chess.com/groups/home/online-tournaments-information-store

Many thanks for quick and clear answers!!