Here is some more information about the non-working burner. It turned out that the burner did not like Philips DVD-R disks. I got a replacement burner from our IT-department, and it still did not burn the DVDs. Then I tested some other types of DVDs; TDK DVD-R and Verbatim DVD-R, and it turned out that they both worked fine. So is it possible - or plausible - that a burner is sensitive as to the type of DVD brand?