Cannot connect to external FTP server after SP1 install

I am running Server 2003 Standard, using it as an all-in-one server (IIS,
router, remote access, exchange, etc). I upgraded the server to SP1, and
since then I cannot ftp to my (external) hosting provider's site. I've tried
from the server itself, as well as from 2 clients running XP SP2. The server
& clients give different but similar error messages, and are unable to
retrieve the file list on the remote FTP site. I'm running WSFTP, but have
also tried the command line FTP with the same results.

I know the problem is due to the upgraded firewall, because if I turn off
the firewall, it works fine from the server (but get the same errors from the
clients).

I also saw a similar post saying active FTP works, but passive doesn't - in
my case, both fail.

Any suggestions would be appreciated. Thanks.