Why dont you try divxtodvd, i had problems with nero, i had same problems as yourself! to be honest i think its the make of your burner, nero is very fussy as to which burner you can burn with! i decided to ditch Nero altogether and now iam using divxtodvd which is an excellent program for converting files it recognises the media you have inserted and converts to fit onto the media you are using whether it be 1 or 2 movies!!
need info on how to get it pm me!