Can't save pages anymore.

[Johnnie Torch]

I'm a cartoonist who uses GIMP to create my comics. I suddenly haven't been able to save my work. I tried some of the obvious workarounds to get past this. (Updated from GIMP 2.10 34 to 36. Tried renaming files, moving pages to other folders, etc.) Nothing seems to work and I'm beginning to think all my work is lost.

I'll attach the screenshots of the messages I get.  The first one I get when I bring up a file says "Could not read the contents" Then when I try to save, it says "Error Truncating file. Permission denied"

         

I would appreciate any advice, but bear in mind I will need it explained like I am 5 years old. (Not very tech savvy, I'm afraid.)

Thanks in advance,
JT