Are you able to burn to a folder on your hard drive rather than directly to a disc?
The Vobulator is a module that performs the function of gathering up your navigation settings, and then arranging everything for the creation of the VOB's (Video Object), the building blocks of a DVD.
Something is causing a problem in that process.
As a start, along with Steve's test, do you have a Stop Marker at the end of your Timeline? If so, remove that, as it is not necessary, and can definitely cause issues.
Is this the same issue that you are presenting today in a new thread here
If so, please refer to my reply there.
The bottom line in my reply there is to remove a stop marker which I suspect is at the end of the last item on your project's Timeline.