Please list the contents of one of your compressed VIDEO_TS directories. Does it contain:
Are you SURE you're choosing the VIDEO_TS folder?
In Toast, be sure to have first selected "DVD" from the "Other" menu. Any other way of burning a disk will simply copy data onto the disk, instead of triggering the special DVD flavor that you need.
When it's showing DVD, also make sure you have your disk set up as follows:
-- click "New DVD."
-- Where the new "Untitled DVD" name appears, feel free to rename your disk using capital letters and underlines instead of spaces.
-- Click "Add Folder," and create one called AUDIO_TS.
-- Drag the newly compressed VIDEO_TS directory from Finder into Toast's center window. Make sure it's on the same level as the AUDIO_TS folder, and not inside it.
-- Check the contents of the VIDEO_TS folder to make sure there isn't a .DS_Store file there -- this is something OS X uses in Finder, and should be removed in Toast.
-- Final DVD file size shouldn't show more than 4.4 GB.
-- Now burn!