Unable to set a firewall rule on the plesk admin interface

[ergos]

Hi all,
I am trying to set a firewall rule on the Plesk admin interface but when I activate it I get connection error and then Plesk restore itself without the rule.

Any idea? And yes, I am not using APF and I don't want to use it since I think that if Plesk ships with a built-in Firewall it must work...

Thanks again.