Daemons?

That was me. A daemon is an application that runs in the background, usually listening for an event to which it can respond. Some device drivers fir this description category. So if you've installed new software / hardware on your pc between successful copies and present situation, then you might care to look at the cpu/resource consumption of such applications. Generally speaking, normal daemons that run on your pc like anti-virus #####ers don't interfere with cd copying. But I've seen one (for an ISDN card) that consumed 80% of the CPU when idling in certain circumstances.

In simpler terms, and this may be what's happening, if you happening to be doing something on your pc whilst the copy is running, then you could be stealing resources from Nero and data is unavailable at the point when it next needs to write to cd-rom.

General rule: when copying to a CD, don't run anything else.