AWS SFTP error Disconnected: No supported authentication methods available (server sent: publickey) on filezilla

I've created a new EC2 instance on Amazon AWS and tested the TTY with mindterm. Everything worked well, so i set up apache 2.2 on the instance and decided to connect by SFTP using FileZilla (configured a new site with the correct URL, the default user and SFTP as protocol). I've downloaded the .pem, converted it into .ppk and set it as key in FileZilla. When i tried to connect, it gave the following error:

    Disconnected: No supported authentication methods available (server sent: publickey)

I've manually checked the keyfiles and everything is correct according to http://ift.tt/1B41OLw

How can i solve this?

PS: Sorry for bad english... it is not my native language

EDIT: PuTTY gives the following error: Unable to use key file "C:\Users\S▒rgio\Downloads\key_netnografia.ppk" (OpenSSH SSH-2 private key) (the ▒ was supposed to be an "é")