title: can't add file to git repository but can change / commit
body: <p>here is error :</p>
  
  <pre><code>git add .emacs
  error: insufficient permission for adding an object to repository database .git/objects
  
  error: .emacs: failed to insert into database
  error: unable to index file .emacs
  fatal: adding files failed
  </code></pre>
  
  <p>how can I fix it ? what's wrong with it ?</p>