I've got a program that take advantage of FTP Client, it's running in a number of machines also it stoped employed in among individuals machines.

Making the debug I can tell that the issue is on listFiles(), listNames()... However it work's perfect giving me the title from the directory after i make printWorkingDirectory() or after i make FTPReply.isPositiveCompletion(ftp.getReplyCode()) it brings me the real value.

I've also made ftp.enterLocalPassiveMode(), ftp.setFileType(FTPClient.BINARY_FILE_TYPE).

I am lost, are you able to help me?

Seems like the information connection is blocked - probably inside a router or firewall. You have to possess the machine "behind" a NAT device function as the active one.

What's the exact network configuration between your two machines you experience?