Nec 6750A don´t recognize burned verbatim DVD-R

Hi, i have a laptop with this dvd-writer and i use to use verbatim dvd. But with this writer i can´t use them because, after burn one, the writer doesn´t recognize it, it shows me a blank dvd. I have the 2.61 firmware in a packard bell laptop (in its homepage shows the writer is a liteon 833S by the way :confused: ) and nero 6 to burn the dvds. Anyone knows how to repair this?