I've got a Filezilla FTP server running on Windows Server 2012 accepting passive transfers. The problem is that intermittently, the passive ftp quits working and giving 425- Connection Refused errors.
I've tried restarting the FTP service and restarting Filezilla but the only thing that I've found to fix it is to reboot the server. It will then work for anywhere from 1 - 4 days without a problem and then starts failing again.
I have Windows Firewall turned off so it's not an issue.
What else could I check?