Try using active mode and / or update to a more recent SmartFTP version (see my footer).
Thanks for your response. I had started with V2 as I was planning to renew my license, but wanted to make sure it worked first!
Here is the log from V2 with active mode.
[08:04:49] SmartFTP v2.0.992.40
[08:04:49] Resolving host name "nn.n.nn.nnn"
[08:04:49] Connecting to nn.n.nn.nnn Port: 21
[08:04:49] Connected to nn.n.nn.nnn.
[08:04:49] 220 Titan FTP Server 5.05.323 Ready.
[08:04:49] USER username
[08:04:49] 331 User name okay, need password.
[08:04:49] PASS (hidden)
[08:04:49] 230-Welcome username from nn.n.nn.nnn. You are now logged in to the server.
[08:04:49] 230 User logged in, proceed.
[08:04:49] SYST
[08:04:49] 215 UNIX Type: L8
[08:04:49] FEAT
[08:04:49] 211-Extensions Supported
[08:04:49] COMB
[08:04:49] MLST type*;size*;modify*;create*;perm*;
[08:04:49] SIZE
[08:04:49] MDTM
[08:04:49] XCRC
[08:04:49] REST STREAM
[08:04:49] AUTH SSL
[08:04:49] AUTH TLS
[08:04:49] CCC
[08:04:49] PBSZ
[08:04:49] PROT
[08:04:49] EPRT
[08:04:49] EPSV
[08:04:49] DQTA
[08:04:49] 211 End
[08:04:49] Detected Server Software: GlobalSCAPE Secure FTP Server
[08:04:49] PWD
[08:04:49] 257 "/" is current directory.
[08:04:49] TYPE A
[08:04:49] 200 Type set to A.
[08:04:49] PORT 10,0,0,100,11,170
[08:04:49] 200 PORT command successful.
[08:04:49] MLSD
[08:04:49] 150 File status okay; about to open data connection.
[08:05:10] 425 Unable to open data connection.