Machine won't read DVD-R?

[jedooley]

I bought a new Dvd Recorder. A Panasonic DMR-e50. It burns fine and plays the disks I have burned fine. But when I take that disks to my other DVD players it won't read the disks? These machines are less than a year old and should be DVD-R compatible. My friend made me a DVD-R on his PC it plays fine in my other players?

Does anyone know why my DVDs burned in my DVD recorder will not play on other machines?