The message "Connection reset by peer" means the server closed the connection. The cause could be a TCP timeout, a lack of disk space, ETC.
- Try transferring the file using FTP without using Java, using a command line utility.
If the same problem occurs, it is definitely not the Java program.
- Make sure the network is not sensitive to the size of file(s) being transferred.
- Make sure the server is not blocking connections from your client after it has already made "N" previous connections or after a certain length of time, E.G. 20 minutes.
- See if your client can establish a persistent TCP connection using another protocol: SSH, etc.
If the problem occurs with the other protocol also, it's likely to be the network.
If you find the issue is caused by a timeout that would only happen if your connection was idle too long, then check this URL:
FTP: "Connection reset by peer"