....to page three here are a few suggestions. Others may now spot your thread and leap in.
Sometimes a reboot between burns is necessary (shouldn't be but there it is).
Otherwise, try reinstalling the Nero software.
Have you tried another disc? You do get a bad one from time to time with either CDR or CDRW. You can use the Nero Tool Kit to check disc quality and to find faults.
You say you can't remember what the error message was. But this is important -- you need to know that as a base fact in order to have a bit of a clue as to what the problem might be.
Don't forget also that errors and the cures are listed on the Nero site.