ftp4j java ftpClient manage connection failures during file upload

Question

I am trying to implement an ftpClient interface which would be able to manage network connection issues. I am using the ftp4j library for this purpose.

I can succesfully upload files BUT i have some issues when a connection failure appears during a file upload process. I would like to be able to re-upload (not append, just start again) the file just after a connection issue terminate my previous upload attempt.

The case is that if i try to re-try uploading the file some seconds or even minutes after the previous unsuccesful attemp i am getting:

it.sauronsoftware.ftp4j.FTPException [code=550, message= Access is denied. ]
at it.sauronsoftware.ftp4j.FTPClient.upload(FTPClient.java:2794)
at it.sauronsoftware.ftp4j.FTPClient.upload(FTPClient.java:2586)

If i wait some time and then re-try, i will be able to upload the file to the FTP server.

Is it some parameter that i could set to my ftpClient:

...
FTPClient client = new FTPClient();
try {
    client.setType(FTPClient.TYPE_BINARY);
    client.connect(ipAddress, port);
    client.login(userName, password);
    System.out.println("Connected to FTP Server!");
    ...
}
...
if(ftpClient.isResumeSupported()) {
    System.err.println("FTP Server supports resume. Trying to upload file");
    ftpClient.upload(localFile, writtenBytes, new Ftp4jListener());
} else {
    System.err.println("FTP Server does NOT supports resume. Trying to upload file");
    ftpClient.upload(localFile, new Ftp4jListener());
}
...

for being able to overcome this "Access is denied" problem? Any ideas what is it causing such an exception? Maybee a server parameter?