The problem is this: <script src="http://w.sharethis.com/button/buttons.js"></script> Try to add this to the body or footer of your site and then remove the link to w.sharethis.com. Because this not a local js it will not be cached and this will show as a js / css error in pagespeed. You could save this as a local file and then change the link from sharethis.com to your local file or you can use a plugin like cache external scripts
hope this helps