Let's see if we can address some of these issues:
You're using PE7, so you are locked into the way that it does its Menuing. It works with Menu Sets, a Main Menu and then the necessary number of Scene Selection Menus, generated as is necessary to accommodate your DVD Chapter Markers. This is done semi-automatically by PE.
The first thing that I would suggest you do is to Open both a Main Menu and its Scene Selection Menu in PS. Regardless of which se you base your design on, the structure must be just as is represented in the Templates in the respecitive "set." The naming conventions must also be followed, so that PE can do its thing. You can add Menu Sets, but you do need to do things, just as the Templates are designed. When you work on your new Menu Set, I'd strongly suggest that you follow along with one of the Templates to make sure that the i's are dotted and the t's are all crossed.
Now, going to your comment:
After experimenting with the short test clip, it seems to be the additional scene buttons that I've added, 7 through 25. In other words, I can burn a disc with the Generic Text Menu, but ONLY when I have 6 or less scenes.
PE will use the necessary number of Scene Selection Menus (Sub-Menus), to accommodate your DVD Chapter Markers. If you have a Scene Selection Menu with 6 Buttons, and have 36 DVD Chapter Markers, it will use 6 Scene Selection Menus from the chosen set.
As no Button can overlap (this is the entire rectangle circumscribing the largest element, or collection of elements in your Button Layer Set), if you have any sort of overlap, you will get errors. Using small elements, one could create a Scene Selection Menu with 32 Buttons in a 4:3 Menu (think that number is correct, but don't hesitate to check it out), and 16 Buttons in a 16:9 Menu. That is a DVD-spec limitation, and not a limitation of PE, or any authoring program.
"Device error - Sense Code (3 57 00) Unable to recover Table-of-Contents"
Sense Code Errors are most often the result of the media. It can be a bad disc, a disc, to which material has already been recorded, or the wrong type for the particular burner. What brand of DVD are you using, and also what type? Does your burner support that type?
When I play the DVD on my set-top player, the "bullets/hilights" in front of the scene name, seem to ghost from adjacent scenes. For example, when I scroll down to, say, the 4th scene, the hilight from scenes 2 and 3 stay on. On the Main Menu, the Play and Scene Selections show their hilight all the time. It looks like someone has simply typed it onto the screen twice with the lower one (the hilight??) indented a few spaces.
This sounds like problems with the Sub-picture Highlight Layers. These, by DVD-spec, can only be 2-bit color, but can have Transparency. This is set by the Menu Color Set. If Sub-picture Highlights are on, when they should not be, it is most likely that their Layer, within the Button Layer Set is set to ON (the "eyeball" is showing). With the design of a Menu, the Sub-picture Highlight Layer MUST be turned OFF. It is then turned ON, when one navigates to that Button. Check the "eyeball" in those Button Layer Sets in PS.
I'm sure that I have missed something important, but these thoughts should get you started. Remember, use the existing Templates as a guide. Do things exactly like that. Also, Steve Grisetti has done series of tutorials on Menu adaption and design for PE. They are available here.
I do have to admit that I would in Encore, rather than PE for authoring, so I am not an expert on all of the nuances for PE. For me, everything is done by hand, where in PE, some is semi-automatic.
Good luck,
Hunt