DVD-R

[codswallop]

Some time ago I copied a gardening DVD (naughty me)onto a DVD-R disc,which I've since lost so I tried to do another but halfway through the burning process the disc was ejected.As I knew it had worked before I tried again and this time all was well.Any ideas as why this happened please????
I was using Nero Express Essentials.

Is there any difference between discs DVD-R and DVD R. Thanks!!!