What happened in Cromañón?

On December the 30th, 2004 a group of approximately 2.811 kids, coming from different backgrounds and with diverse interests, got together to witness the live show of an argentinean rock band known as Callejeros, on a local dancing club called República de Cromañón (also known as Cromagnon.) What was originally planned as a party ended with the tragic death of 194 people, with over 700 kids wounded. What happened there?

Documentary Video: Cromañón, how and why (in spanish, 08:40)