LG RC797T _Finalized dvds will not play on ...

LG RC797T

Dvds that are recorded on this LG RC797T will not play back in this unit nor will it play in my other LG DR1F9H. But it will play in my other dvd players models ( Philips,RJTech & others).
It will play any recorded dvds from my other dvd recorders also the ones that are purchased. But not the ones that are recorded in this unit.
Insert the recorded dvd the LG RC797T reads it, displays on TV screen "VIDEO" and ejects the disc and says unknown format or disc error.