Thanks for the quick reply.
The file size is 4,697,620,480 bytes and Deepburner shows 8,454,144 bytes of space left.
The file is a multispan zip file. 7z lets you pick the volume size in this case DVD 4480MB (it’s a dropdown list - you can’t specify MB just “DVD” etc - and it lists DVD as 4480MB.)
7z is such a widely used zip program I would be surprised if it created a file too larger for a DVD.
I’ll check a 7z forum and then try your idea of new burning sw.