Last burnt DVD won't play in DVD player

[Ketch]

I've been burning DVD's for a while now and haven't had a problem, but the last two DVD's I've burnt (Hostage and Ice Princess) won't play in my DVD player, they only play on my computer. Does anyone know what the problem might be?
This website has been a goldmine for information thus far, but I can't find any information relating to this particular problem.
Thank you in advance.

[LT. Columbo]

first, any chance you have switched media type?

[Ketch]

I haven't done anything different than the previous DVD's I've burnt. I tried playing the problem DVD's in a different DVD player and they seem to work. The original DVD player that posses the problem is able to play other burnt DVD's.

[LT. Columbo]

again to clarify, any chance you have switched MEDIA type?