Error installing pgcrypto extension

I want to install the pgcrypto extension on my postgresql installation on Windows. I found that I just have to call CREATE EXTENSION pgcrypto; but I've got an error : Syntax error on « CREATE » LINE 1: SELECT COUNT(*) AS total FROM (CREATE EXTENSION pgcrypto) AS... (I'm on **PostgreSQL 9.2.4** and I executed the sql line from phpPgAdmin with *postgres* user)