I often edit files without having the right permissions in VIM.
I changed the file and when VIM told me that I did not have the proper permissions to save it, I quit VIM and entered
sudo !! to try it again.
This was of course stupid of me. Currently I try to be more mindful about this kind of problems and to fix them.
Here's the lines that I just added to my .vimrc
" Use :w!! to save as root! cmap w!! w !sudo tee % >/dev/null
When I enter
:w!! now VIM saves the file as root.
I hope I will not encounter this problem again.