Help Making A DVD Backup PS2 Game Please?

[Pancrack]

I'm trying to make a Ps2 dvd out of a downloaded file.
I have an iso of a game and I've burned it to dvd using Nero.
It burned fine but the PS2 doesn't recognise it.
I tried a different game, also on DVD, and that one is exactly the same.

I've successfully done quite a few Ps2 games on CD before, but not tried a DVD until now.

Any ideas as to why my dvd writing is not working?
Could it be something as simple as using the wrong blank dvds?
(I used a cheap 4X DVD-R)

Any advice would be much appreciated.

cheers.