Itunes help needed - Red caution word/box - screenshot included (why is it there and how do I fix it?)

So I bought a TV series from iTunes (no gift card, just debit card) and all the episodes for series 1 were fine (series 2 below only) but there is these 'caution' warnings on all but two episodes of the series - as you can see below.

Question: Why are they there? How can I fix it? Why aren't they all like that? I haven't moved them from their original file location - I've only copied and pasted them to my videos folder and I've done the same with the series 1 episodes, so that really can't be the problem. It doesn't tell you anything out of the ordinary when you click on 'Get Info' - so it wasn't much help at all.

(Also, don't worry about that 'Terminal' episode - it was only downloading from the Cloud - the 'caution' warning was there even before I downloaded it...hmm.)

I haven't tried putting the episodes on my iPod nano yet, but they still seem to play fine through iTunes - the iTunes player is slow anyway, but yeah. It stills plays.

Screenshot of the scenario:

Help would be greatly appreciated! I'm running backups of iTunes, so I really need to know that there won't be any problems later on that can otherwise be fixed just now!