Just to be sure which box do you have a 360 or V6 both boxes look the same but the remotes and software are different, there is a picture Here the reason I ask is that it has been known that some episodes are missing on one or the other boxes.
If it's definitely a 360 I don't know why you can't play episode 1, everyway I try it plays, have you tried going to the Channels list under box sets & movies and dropping down to Sky Max it shows them all as being available. Apart from turning the box off with the switch on the back of the box and letting it restart, (is that what you have already tried), I would try a factory reset if you haven't done so already,
go to Settings > System > Factory Reset
You are given 2 options,
Keep Recordings
Format Disk
Choose Keep Recordings, that way you won't lose your recordings and any planned recordings or series links you've set up, but you will have to sign into your apps such as iPlayer, Prime, Netflix and ITV Hub again, also Match frame rate and Standby power consumption will go back to their default settings if you have changed them.