That's not much information to help you solve the problem.
How are you trying to connect to that Linux machine? With an FTP client program? Or with your own Java program? If it's in your own Java program, then how are you trying to connect? Can you post your source code here?
Is there an FTP server running on the Linux machine and is it accessible (i.e. is there no firewall or something similar between your client computer and the Linux machine that might be blocking FTP)? Are you using the correct username and password for FTP?