ftputil variable behavior (errors 10054, 10060)

Question

Hello I have a simple function below to list all files on a ftp server.

import ftputil
ftp = ftputil.FTPHost("3.xxx.xxx.xx","xxxxxxxx", "xxxxx")
for (Root, dirs, files) in ftp.walk(Root) : #Iterate over remote file
    for fileName in files :
        list[Root+ "/"] = fileName
ftp.close()

Sometimes the listing is done well but sometimes I get the errors : ftputil.ftp_error.FTPOSError : 10054 or ftputil.ftp_error.FTPOSError : 10060

Unfortunately, the server is behind a firewall that I cannot modify. But my questions are, do I use properly the ftputil library ? Do I get these error because I open to many connections ? Is it possible to fix these errors without changing firewall properties ?