Are you burning a DVD or BluRay? What happens if you burn a Prepared File to your hard drive rather than directly to a disc?
What are the source files you're using for your DVD Architect project? It's recommended that you use DVD or BluRAy ready files from Vegas/Movie Studio and that you do not use files directly from your camcorder.
How fast is your processor, what operating system are you using, how much RAM do you have and how much free, clean space is on your C drive?