The easiest way to stop your users accessing one or more of the file transfer protocols is not to install them. During the installation of TTWin3 you will be asked what type of installation you want, Select Custom. In the custom install you can choose to install just the file transfer protocols that you want.If you don't install the FTP protocol you will receive an few error when you start TTWin3, this is because TTWin3 uses the FTP protocol by default. If you install another file transfer, you can select it in Configure | File transfer... You will need to save the changes to your session file (Default.twc), by selecting File | Save.
If you chose not to install any file transfer modules you will need to edit some of TTWin3's configuration files.
Using Windows Notepad.exe, open C:\Program Files\Turbosoft\TTWin3\Ttwin.ini
Change the entry DfltFileTransfer=ftp.dll to be
DfltFileTransfer=
Then using Windows Notepad.exe, open C:\Program Files\Turbosoft\TTWin3\Config\Default.twc
Change the entry FileTransfer=ftp.dll to be
FileTransfer=
You should now be able to start TTWin without receiving any errors.