PS to Opening Post:

Among the things I did to try to ferret out the problem, did a sfc /scannow on C:\ and am in the process of backing up my entire media and Vegas projects D:\ mechanical drive so as to run a chkdsk /r on it. Probably won't fix anything, but no harm in doing so (once in a while, for chkdsk /r is kind of intensive on mechanical HDs).

And it will take a while since it's a 3TB one...

From what I gather running a chkdsk /r on my OS SSD is not a good idea, and not sure chkdsk /f would be of use. I have neat little, fast, old-school defrag program (MyDefrag v.4.31) that has options like "only consolidate empty space". But there again, not sure using regular defrag or that option would fix anything related to VP problem.

I also defrag or use that option only on occasion -- such as before some important backup -- for over-doing it on mechanical drives tends to wear them out.

Bump.

► IMPORTANT ADDENDUM to Opening Post ► 
(Yet General Query of OP Still Stands)  

IT LOOKS LIKE ONLY THIS .VEG FILE HAS THIS PROBLEM (CORRUPTED)

I decided to go and render another far simpler, less heavy .veg.  One based on a creative
"Ken Burns" type pan-zoom, etc. of a still photo with some of my signature fx and
Particleillusion .png sequences. NO problem.

Then I rendered another, more complex project (no double fps events though), and, that
one also rendered out.

So since this appears to be a one-file corruption, is there way to reverse-engineer it or
ferret out the problem -- possibly Render Templates?  For example:

Is there a way to use go into Options/Preferences "Internal" and temporarily hid or
deactivate all custome render templates so only the factory ones are listed and active? 

I don't want to even attempt do that without your guidance.
 

"WHAT ABOUT USING AUTO-SAVED .VEG OLDER VERSION OF PROJECT...."

Yes, I do have some auto-saved versions from before the error and subsequent need to
close the .veg (but no crash occurred oddly enough) 

I'd have go through several of those to find an uncorrupted one, and I'm concerned that
all the corrections and tweaks done since that one will be a major pain-in-the-derrière....
 

WHEN PROBLEM OCCURRED -- AND PERHAPS WHY?

By the way, this can't-render-anything-anymore occurred during an open session of my
current 8 or so minutes long .veg project.  That is, I was doing test renders of sections
as I tend to do just fine, then suddenly, no go.  

There is a mix of media in this project. So as to make crisper pan-zoom, etc. on existing
29.97 .m2t files from my older Canon camcorder, I re-rendered those events at douple
fps, 59.x.  I sometimes have preview problems with those, but again, before now, no
problem rendering out.

I've also attempted to change the .veg project settings (set at 59.x fps due said files)
back to 27.x, before render, still no-go.

Are these 5.9x fps files possibly causing the problem now, for whatever ? reason?
_____________

All that said and as hinted to at beginning here, the general OP's subject of what to backup for a full reinstall stands. Just in case something goes wrong on a global software level with my VP10.

Pardon long-winded posts, but better be detailed than not.

~ Philip

Thanks, and I get that. But it's not answering the which-folders-and-files-to-backup question.

I've been using Vegas since v6 and have built up fx chains, render templates and some Preferences settings -- I've been able to transfer those over from v.6 to v.8 to v.10 for as I recall (correctly or not), the new version somehow tapped into what was already installed. Or minor adjustments were necessary.

Or under my original 11 y.o. member name "Soniclight" (no 2.0 - had to add that for somehow my original profile was not restored) I had inquired about this issue and found a solution.

I don't want to have to start all over with those. Lot of work put into them.

Migrating or transferring personal settings in Vegas is a mess. This comment has some pointers. Obviously you need to change the folder paths depending on which version of Vegas you're using.