Thank You @phpcodemonkey
This worked for me.
Had to delete a load of ports to set this up but is now working i was using all tcp ports.
So, there is a workaround available for this issue (The local ports between x and x on IP x.x.x.x have been added as virtual server already, please try another one.):
It seems that it is possible to get the port forwarding to work (as in it does forwards ports at the network). However, the UI to set forwards up doesn't work very well. This issue comes from a bug caused by a naive test in the JavaScript validation (so it could be fixed by a firmware update!).
The workaround, while a little annoying, seems to work reliably. You need to add the required ports in a sequence of lowest to highest, within each IP address/protocol combination. So, for example, let's say I want to add ports 4500, 500, 8080 for UDP to IP 192.168.0.10 - to achieve this add them, so the overview table results in the sequence:
192.168.0.10 500-500 500-500 UDP
192.168.0.10 4500-4500 4500-4500 UDP
192.168.0.10 8080-8080 8080-8080 UDP
The annoying part is that if you want to insert a lower numbered port, you have to delete the higher ones for that IP address, add the lower port sequence and then re-add the higher ones back in - a little tedious but it works none-the-less.
