FTP issues on LAN

SBS2000, 2 nic
clients are xp and 2000

Have a Sharp Multi unit that when we installed worked with all clients. We
now have one client that we can not scan at the Sharp and send scan to
desktop software.

This client also had JAVA issues which I thought were related, but
installing JRE solved those. Still Sharp scanning no go... Upgraded it
from Win2000 to XP Pro with same results...

Have trouble shot with Sharp tech and have basically concluded that this
client is having ftp issues on port 21 (which is what it needs) that doesn't
allow it to communicate with the Sharp Unit that acts as an ftp server for
the LAN for scanning and sending image to clients desktop Sharp software.

On this client from cmd window c:>, ftp> open 192.168.16.11 21 enter.
Returns: > ftp: connect :Unknown error number

On all other clients (substituting their ip)
Returns: Connected to (IP).220 "client"."domain".local FTP server <Version
SharpDesk-0.5> ready.

The only thing that I can think of is that this is the only client that I
currently have set up for VPN. Whereby user establishes a VPN connection
from his home computer to the SBS server and initiates a TightVNC to control
his pc.

Sharp has basically said that there is nothing more they can do...

Any ideas on how to go about identifying what is happening with ftp on this
client on LAN?