Benq DW1610 writes faulty DVDs-Solutions?

My problem is that when copying movies and burning with Nero 5.5.10, the DVD is writen completely and ‘succesful’ however, when Nero scans the disc it finds errors and the dvd is useless. I have already writen 17 discs succesfully while 10 other discs have been unsuccesfull. This makes about 1 success for every two trials. Is that normal to have such high error rate? I wonder if this is caused by the drive or is it due to the media. I’m using a generic DVD+R brand, cheap, which should be burn at 4X. I’m burning them at 2.4X but still the problems come. Any help is welcome. I saw that a new firmware is available (B8M9). I will upgrade and report. Please help.

Ok. So I upgraded the Firmware to B8M9 and burned the DVD at 4X (the same title that failed three consecutive times before) and guess what: It was burned succesfully! Still, I will need to do more dvd copying to make sure it is consistent and not a random success event. Will post latter.