Error in Preview and Publish

I am running into this issue in a 4.5GB, 7-scene, 200+ slide project. I have been troubleshooting for 2-3 hours today already.

Problem:
I try to preview selected slides; it starts loading, then gives me the error message.
I've been developing this course for months, and the issue started today after tweaking a few slides and then trying to preview them. The course is due in two days.
The issue happens 90% of the time - sometimes, it will let me preview some selected slides, but most of the time, it won't. There's no consistency as to which slides work and which ones don't.

Troubleshooting:
Restarted SL (many times)
Restarted PC (many times)
Uninstalled/reinstalled SL (twice)
Tried previewing different slides/different scenes (with only about 10% success)
Reverted to a previously saved version
*Created a new file and moved each scene in one by one

Other relevant info:
I am using a built-in disk, not a network drive
My computer is over-powered with plenty of free space
I don't leave SL open when I leave the computer or put it to sleep
I update SL every time an update is available.

Results so far:
*The only thing that seems to show any success at this point is coping and pasting all seven scenes into a brand new file. All scenes made it in, and the issue hasn't replicated itself yet. This would seem like a win, but it comes with a major caveat...
I was hoping that after moving in an allegedly corrupt slide, the error would appear, so I could pinpoint it and fix it in the original file. However, it didn't. The new file has no errors. Does that mean I need to spend the time re-creating my player and all the customization that didn't transfer over? I want to do everything I can to avoid this because it's adding hours of work late in the game, and I'm very concerned something will slip through the cracks. Is there any other way I can still make the original story file work?