Allow clients access to internet ftps sites

I have a client that says he is trying to access a secure ftp service
using port 990.
The user gets these command responces. I have removed site addresses
and usernames etc. at users request for security.

Réponse : 220 Welcome to XFB Gateway FTP server
Commande : XXXXXXXX
Réponse : 331 Send password please
Commande : PASS XXXXXX
Réponse : 230 User logged in, proceed
Commande : FEAT
Réponse : 211-Extensions supported
Réponse : 211- SIZE
Réponse : 211- MDTM
Réponse : 211- AUTH TLS
Réponse : 211- PBSZ
Réponse : 211- PROT
Réponse : 211 End of feat command response
Commande : SYST
Réponse : 215 UNIX XFB/UNIX
Commande : PBSZ 0
Réponse : 503 Bad sequence of command
Commande : PROT P
Réponse : 503 Bad sequence of command
Etat : Connecté[English] state : Connecetd
Etat : Récupération de la liste de
répertoires...[English] getting folders list
Commande : PWD
Réponse : 257 "/" is current directory.
Commande : TYPE A
Réponse : 200 Command okay
Commande : PASV
Réponse : 227 Entering passive mode (xxx,xxx,xxx,xxx,xxx,xxx).
Commande : LIST
Erreur : Inactivité détectée ![ENGLISH] Inactivity
detected
Erreur : N'a pas pu récupérer la liste du
répertoire[ENGLISH] Can't get folders list

The 227 Entering passive mode (xxx,xxx,xxx,xxx,xxx,xxx) thwe first four
decimal numbers appear to be the IP address of the destination server I
do not know what the following 2 sets of numbers are unless they make
up an IP v 6 address

The firewall is a PIX-525 running 6.3(5) OS

I don't have any ports blocked for outgoing traffic.

I do have fixup protocol ftp 21

I have limited expertise in this as I am covering for our usual network
engineer, but need to try and resolve this problem as soon as possible.

Thanks to anyone who can point me in the right direction to fix this,

Marcus.

.