git "fatal: .git/index: index file open failed: Permission denied"
From the verbose output, it appears that the permissions of the
.git/index while might have gotten corrupted.
Confirm that this is the case by doing a
ls -al .git/index followed by a
chmod 644 .git/index to fix it. Then try running the
git add command again.
It turned out to be a (Windows) permissions issue. What worked was simply creating a copy from within msysgit of the original folder and using that (i.e.
cp -rvf original original-bkup).
A reset of the permissions on the original folder should have worked, but didn't.
Mark: If you have this error in Android studio, just restart your android studio and this error will be solved. I guess that This is because of some 'cache' or 'bug' of intellij idea.