The card "Magician's Circle" doesn't work when you attack with a Spellcaster. The text says: "When a Spellcaster-Type monster declares an attack: Each player Special Summons 1 Spellcaster-Type monster with 2000 or less ATK from their Deck in face-up Attack Position." It just works when the opponent attacks with a Spellcaster, but it should also work when you attack.
if one of player's all monster zones occupied, magician's circle cannot work
Magician Circle is a trap card, when set it, you must wait 1 more turn after that you can active the effect