Can't load sftp21.dll module with CuteFTP Professional

I was having a heck of a time getting Globalscape CuteFTP Professional 8.3 working for SFTP (FTP over SSH) sites. Since the server on which I was installing the software didn't need any of the "Productivity Tools" listed in the installer, I de-selected that hive.

After installation everything appeared to be working however when I tried to connect to an SFTP site I was greeted with the following error:

*** CuteFTP 8.3 - build Oct 22 2008 ***

STATUS:> [10/28/2012 6:32:47 PM] Initializing SFTP21 module...
ERROR:> [10/28/2012 6:32:47 PM] Can't load sftp21.dll.
ERROR:> [10/28/2012 6:32:47 PM] SFTP21 module was not initialized.

There is literally nothing on the Internet related to this issue other than "registry fixing" software. So I broke out Process Monitor (procmon.exe) to see what was happening. It looked from procmon that it was finding sftp21.dll just fine. But I did notice that it was trying to find zlib.dll which was nowhere to be found.

I checked on another server on which I know SFTP worked and there was zlib.dll in the CuteFTP Pro installation folder. I checked the CuteFTP installer again and in the Productivity Tools option was an option called "Compressed Transfers." I re-installed CuteFTP Pro with the "Compressed Transfers" checked and looked in the installation directory and there was zlib.dll. I retried my SFTP connections and they now worked.

So it appears that sftp21.dll actually depends on zlib.dll so if you're having this issue make sure "Compressed Transfers" is selected if you want to connect vi SFTP/SSH.

This issue may be fixed in a newer version of CuteFTP Pro, but we're standardized on version 8.3 so that's what we have to deal with.

There you go. Hope this article helps others.

Flux aka Andy.