Welcome to the forum
Hmmm, ConvertX produces playable discs for me (I use ConvertX 2 though, couldn't get on with the latest version).
Does the Sony give you an error message?
Might be worth trying:
- A different disc brand
- DVD-R discs, if you're using DVD+R
- Lowering the speed you burn the discs at, by just a notch, if you're burning at maximum speed.
- A different prgogram, such as the free DVD Flick.