My problem is if I select search from the remote and look for a programme on demand then select it to play the search freezes and requires switching off and on again but still have the same problem. Also selecting ITV hub again the box freezes, this is a new box.
I have just tried with my 4000t (Top Gear) and although it was painfully slow to open up the relevant on-demand apps (iPlayer and UKTVPlay after a black screen for about 10-15 seconds) both worked as expected.
Which particular program are you attempting to play?
With the set in the usual view position try pressing the search button on the remote, then enter the name of what you want to watch and a list appears. Select the one you want to watch. This is as far as I can go after this the box hangs/freezes and has to be switched off.