Unable to Read .tvg

I just started using Harmony Essentials, and have been unable to reopen a saved project. I keep getting this message (see attached). What’s going on?

Did you check if the file exists?
Are you able to load in in the “Play” module of Harmony?

What can you remember about the history of this drawing - what was done in the software?

Movie files are made using a codec (converter). If that codec is not readable by Quictime then Harmony can’t convert the image to TVG format. Also if the movie file is too big you may be running out of memory. You should perhaps contact support and have them connect to your system to reproduce this.

Alternately you can convert your movie to a series of bitmap images and import these instead.

My copy of TBHarmony is also unable to read tvg files.

I hand-animated a rough test with the brush tool in two individual Drawing layers.
I was scrolling back and forth on the timeline when i got a message like jerdman20.
I checked my project folder > layer folders and all the tvg files were there.
I returned to TBH12, scrolled through the timeline and I got multiple messages, just like the first one.
I restarted TBH12. When I opened the project again, all my drawings were gone from two Drawing layers. The tvg files were also gone.
I used this technique for 5 years with no problems in TBH10; My layers (and thus my folders) have the proper naming conventions: “a-z”, “A-Z”, “0-9”, “_”, and “-”. They are properly stored in the project folder. I saved my work multiple times - and possibly after I got the warning (so it’s reasonable to assume that when TBH12 couldn’t read the tvg files, and I saved it, it erased them).
But how could it not read the tvg files in the first place?

I’ve also discovered this:
If I import a movie file (imported as TB bitmap drawing conversion = tvg files) TBH12 doesn’t recognize the tvg files associated with the movie after I Save the file.