You left off the installation method for each of the servers. FTP has had bugs and requires configuration differently based on the installer. Vicidial itself merely assumes FTP will work. But the installer (be that YOU or some installation script, or a combination thereof) must actually provide functional FTP.
You also didn't mention whether you tried to log in as the FTP user manually and demonstrate that (a) FTP is actually running and (b) your FTP user has permission to read/write.
A couple other things are important: Are you sure the Sending server has network access to the receiving server?
Testing stages:
1) Log on to FTP on the server hosting the ftp at the CLI (ftp localhost). Success proves FTP is running and your credentials are valid.
2) Log on to FTP from your workstation (WinSCP? Some other FTP client?) and upload a file. Also create the RECORDINGS and REPORTS folders if they are not already present. Success proves read/write and external access.
3) Log on to FTP from the Sending Server to the IP of the receiving server (ftp xxx.xxx.xxx.xxx). Success will prove access from the sending server.
4) Execute the FTP cron job from the command line with switches "debugX" and limit the transfer to 1 file. This should show you any problems still remaining.
5) If that last step worked: Ensure the URL from that lead's "modify lead" page works properly before fully activating the system. Modifications to the astguiclient.conf file may be necessary to make the links generated by the Vicidial interface will work seamlessly to access the new audio files at their new location. Limiting to 1 file at a time allows you to fix problems before firing it up and letting it transfer ALL the files.
Failure of any of these stages requires a fix before continuing. The fix will depend on your OS and version and installer. FTP, however, is a standard package on all OSs. Specific steps to a Vicibox ISO installed system differ from install to install (but make no mistake: any functional FTP in the OS on that server will suffice, you don't need to use the Vicibox-installer packages, any will do if you get it running).
Happy Hunting