Webmin : Backup configuration files "Firewall Linux " Failed

Operating system: : Linux Debian 9
OS version: : 4.9.0-17 amd-64

Helllo everyone, (sorry for my english)

I installed Webmin 1.984 on Linux Debian 9 4.9.0-17 amd-64.

By Webmin - Backup configuration Files - Restore now : Linux Firewall - Uploaded file, I restored a backup of Linux rules. It is OK, the rules are in Networking - Linux Firewall

But, when i want to make a backup by Webmin - Backup configuration Files - Backup now : Linux Firewall - Download in browser, i have this error : Backup failed : No modules provided any existing files to backup!.

On Network - Linux Firewall, the IPTables Firewall is : /etc/iptables.up.rules.

I don’t know why the backup configuration file “iptables.up.rules” if failed. Can you help me ?

Thanks a lot in advance.

Olivier