Can't access ISPConfig from public ip

Hello everyone, I've a peculiar problem related to ISPConfig. I can access the ISPConfig installation from local network (https://192.168.0.100:81) without any problem but for some reason I am unable to do so from public IP (https://24.86.xx.xx:81). I've tried everything I know to fix this but nothing seems to help. The port on the router is forwarded. This is what I get from FF when try to connect through public ip:

Any help is much appreciated.

 

Ok, I put this system on DMZ and it worked. Still no idea what was blocking it.

 

I guess the router's firewall was blocking port 81.

 

Are you using cisco? It could be either router's firewall or the NAT problem.

 

Since you are using https: just make sure that you are also forwarding SSL port on your gateway. I think it's port TCP 443.