Also had this problem but only after the box was powered off and back on (using the remote control power button). Resolved by changing the HUB so the Humax was always using the same IP address
Just got this box which I am using with a BT Home Hub 4 via wireless. Connected to the hub ok and OnDemand working. Powered the humax off using remote and back on and although still showing connected to the network, OnDemand gave the Incorrect Link message.
Went to the Home Hub configuration via the web on my PC, Advanced Settings, Home Network. Found the Humax in the list (via MAC or IP address) and ticked the box to say always use this IP address.
Seems OK now even after the box is powered off and back on