"A connection attempt failed..." - host support staff cannot duplicate

Please help! The other posts on this general topic don't solve my problem, which has an odd wrinkle.

I connect to a number of servers (to do website updates) from a number of computers in different physical locations. Two are Macs running Fetch; one is a Toshiba w/XP running SmartFTP.

The servers are operated by different host companies.

All FTP programs and all computers have been connecting to all the servers for years with no problems.

Last month one of the hosts moved one of my websites to a new DNS. Of course there is a new address; the password is the same. The Macs can connect to the new server with Fetch. The Toshiba w/SmartFTP cannot connect, I get the error:

[12:01:25] SmartFTP v2.0.1001.9
[12:01:27] Resolving host name "xx.xxx.xxx.xx"
[12:01:27] Connecting to xx.xxx.xxx.xx Port: 21
[12:01:48] A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.
[12:01:48] Client closed the connection.
[12:01:48] Cannot login waiting to retry (30s)...
[12:01:48] Active Help: https://www.smartftp.com/support/kb/58

Toshiba w/SmartFTP has no problem connecting to my OTHER servers, the only problem is the one with the new DNS.

The host's support staff cannot duplicate the error with their SmartFTP, they say it connects as expected.

My security info: My Windows Firewall is On, SmartFTP is listed as an Exception. I have Norton AntiVirus but not Personal Firewall. I have Peer Guardian, but it doesn't interfere with SmartFTP on other servers.