Wordpress 3.9 update editor not working

New version just out 2 days ago (16/04/14 I think) and I update one of my sites straightaway.

Looks like lots of users are reporting the same issue of update - both the visual and text editors are greyed out and completely inaccessible

Quite a few posts yesterday on this and most useful fix I found is http://bit.ly/1pfBFp5