Vsftp passive mode configuration

Hi,
I'm trying to configure a vsftp server on one of my ec2 instances but when I try to connect via a ftp client in passive mode I receive the error message "Server sent passive reply with unroutable address. Passive mode failed."

I have added to my vsftpd.conf file the following lines

pasv_enable=YES
pasv_min_port=1024
pasv_max_port=1048
port_enable=YES
pasv_address=xxx.xxx.xxx.xxx

and I have configured the ports 20,21 and 1024-1048 in my security group.
What am I missing?