Why is git erroring with 'Assertion failed' on git add .?

Question

I forked a repo, then cloned it to my Mac into a /YATC directory. I had a previously-created Xcode project (TwitterTimeline) in another directory, which I copied in

Answer 1

Not sure exactly what's happening but I was in the same situation

1. I moved one git repo inside another
2. deleted the .git dir thinking it would become a regular subdir
3. tried to git add -A .
4. got the weird error message

I got around it by renaming the subdir, doing git add from a parent dir, then renaming the subdir back to the original name. Somehow that seemed to get git back in a working state.