Have you updated 12 to 12.1 yet using an opened project's Help Menu/Updates? Is your Windows 7 32 or 64 bit?
What is on the Timeline destined for the Publish+Share/Disc/DVD with burn to Folder (4.7 GB), or is it Folder (8.5 GB0?
In the burn dialog, what is the Space Required and Bitrate (with check mark next to "Fit Content to Available Space")?
What is the save location of for the Folder (4.7 GB) which contains the OpenDVD and VIDEO_TS Folders? How much free space is at that location?
How much free space is at the location for the Encoded Files Folder (location found Edit Menu/Preferences/Scratch Disks in the Disc Encoding category)?
Are you doing the burn to folder because you prefer it or is it because the burn to disc DVD-VIDEO on DVD disc will not work?
You wrote that "It will do AVCHD and others." Is that for the same Timeline that will not do the DVD (for DVD-VIDEO)?
Let us start here and then decide what next based on the details in your reply. And, questions or need clarification on any of the above, please do not hesitate to ask.