Twitter App - Can only add Tweet to Schedule via Admin User

Hi, I have set up the Twitter app successfully on my clients CMS but have found that although I can easily add a Tweet when I am logged in as ADMIN, when my client logs in as Editor, the Add button is available in Schedule but when he clicks on it takes him back to the Feed page. I have looked at the permissons under USER/ ROLE but can't see anything obvious that will fix this.

Any help or advice you can give me will be much appreciated. :-)