As above I had the same problem and then checked WordPress Codex and found the solution (certainly in my case anyway. Basically wp_head(); must come before the closing /head tag. In my case it was at the top of the head. I put it to the bottom and it worked immediately. As per:-
/* Always have wp_head() just before the closing </head>
* tag of your theme, or you will break many plugins, which
* generally use this hook to add elements to <head> such
* as styles, scripts, and meta tags.