In most cases you get this error message if the forwarding port was already forwarded by another forwarding rule.
If you host the Server at Home please take have a look into this Thread: [Solved] Hosting a TS3 Server at home - #20 by Rikku
In most cases you get this error message if the forwarding port was already forwarded by another forwarding rule.
If you host the Server at Home please take have a look into this Thread: [Solved] Hosting a TS3 Server at home - #20 by Rikku