problem with LG DVD Combo Drive--->>GCC-4521B

i hav the above mentioned combo drive

reading and writing into cd's aint a prob

the drive also reads the DVD's from DIGIT perfectly

but the prob is when i got DVD's burned from a friend's DVD burner
they are not being read(the DVD is not being recognized)...his drive could read it

i hav tried all the brands....MosearBaer, Sony, Imation etc

DMA on my drive is enabled
i hav cleaned the lens
& i hav upgraded to latest firmware version

any ideas folks....???
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any ideas junta....???