BT Business Hub - Changing IP Address Range?

[flashsnaps]

Hi,

 

I have a BT Business Hub which we've been given by BT as our Draytek has gone wrong. Temp solution until we have some more funds.

 

 

The default range for the router is 192.168.1.x

 

 

Our network is on 192.168.20.x

 

 

 

I have gone into the Router, Settings > LAN > theres an option to change the IP Address to manuel and disable the DHCP. But when I click Save it says error.

 

 

But doesn't tell me what the error is????

 

Never configured one of these, is there a setting I am missing elsewhere?