I have been using 3CX for some months now. Running V12 SP6 Intermediate problems with 'No rdp packets'error. All the settings as per all the forums have been altered and checked. Port forwarding, firewalls, NAT all of that. Finally, after we set the correct ports and NAT and all powers that be it started to work again. I thought all was going well for a few days until one morning whilst doing my usual "call the number from my mobile to see if everything works' trick and there was no audio when connected to the IVR. If i changed the settings so that the incoming call would go straight to an internal extension then all would work. But when having the incoming call go to an IVR, it would connect, but no audio. Created a new IVR, restarted the services, all the usual fault finding tests. Finally after reading a few threads i downloaded and installed k-lite codec standard. And wouldn't you know it, it works again. Looks like it was the audio driver/codec on the pc.