ISA 2004

I am using smart ftp in pasv mode logging onto an external site. We are running ISA 2004 and I am using proxy client to open all ports. I have made sure ports 21 and 20 are open out and in and I still get:

"an established connection was aborted by the software in your machine" this happens after authentication.

I have tried pasv and post modes.

Any ideas? It may be isa 2004 but it may be smart ftp. What do you think?