It worked on the single-layered discs, and just one DL disc. I've just set to the appropriate speed. Thank you Lightning UK!!
I uninstalled the drive and restarted the computer. And got burnt the DL. Tried to burn 2 different dvd9 discs, using the same proccess and got failed.
Also, I think it could've been associated with the recent temperature that the notebook got after burning some discs, so that's a reason I could explain for rejecting burning a DL disc.
I'm wondering if I buy an external DVD-RW drive I'll successfully burn all the DL DVDs. Just like this one:
http://produto.mercadolivre.com.br/MLB-438865731-gaveta-p-dv...nd-com-conexo-e-sata-e-usb-_JM
any opinions?
anyway, thanks a lot for the help!