+R DVD Back up isnt as compatible as DVD-R. Thats probably the reason. Either that or you are using a brand of media that is unsuitable. Some of the cheaper brands are useless in Home DVD Players.
Ritek G04's are good, Datawrite new yellows, think they are DVD-R though, Traxdat and Verbatim are also very good. Traxdata use Ritek dye, so they might be the most reliable.