I'm an engineer for a hosting company and we use a Cisco ASA5505 as a vpn endpoint for quite a few clients without an issue. We are using the ASA as an endpoint for a client's direct circuit to us and are experiencing problems with FTP. When using an FTP client it gets to the LIST command and errors out. I've tested the on the other side of the circuit which is fine. We are not running any type of VPN and the access list is wide open. I've attached a copy of the error. Previously to switching to us as their Internet source they had no problems accessing FTP through DSL. Thanks for any insight.
FTP uses both ports 22 and 21 so I wouls start by making sure you can open a connection on both these ports from the client to the server and vice versa. Another thing you could try is running the FTP client in passive mode - there will be a setting somewhere to do that. This sometimes helps when running FTP through firewalls and/or proxies