Dual layer problem with sony dvd (Sony DW-G120A / DRU-120C)

[qanda]This thread is about the Sony DW-G120A / DRU-120C. Click here to see full specs[/qanda]1>THE WRITER FUNCTIONS WELL…

BUT IT DOESN’T READ DVD-9…
i.e. DUAL LAYER DVDS:confused::a

2>DIFFERENCE BETWEEN DUAL LAYER AND DOUBLE LAYER DVDS…

What specific “DVD-9”??