Windows 7: Recorded TV not playing

Ok, so here is a puzzler..
I'm running Windows 7 Ultimate, using a dedicated box (new micro) to view on flat screen.
In 2009 using a similar setup I recorded from a TV tuner about 80+ episodes of X Files. I have last found time to actually watch some of them.

I look in 'recorded TV' find an episode and start to watch. All is well.. then about half way along it stops...! "Unsupported file. MC cannot play the file. MC does not support this format"

Well its recorded in their own format (albeit one used 3 years ago) and it did an ok job up to that point.

So why decided in the middle its doesn't like it?

I can live without X files... but getting half way then... nothing is bugging me.

So far tried 5 shows same happens each time.