Cache problems, site not loading correctly

With my site, http://www.dutchreview.com , I have some difficulties for several days now. The homepage is displayed incorrectly, and shows a 2-weeks old article.

It appears to be something with the cache (im quite a moron with these things I’d have to admit). And in the back-end it shows the following warning in red:

Open Graph Warning : /sites/dutchreview.com/www/wp-content/plugins/nextgen-facebook/cache/ is not writable.

So, quite a problem here, anyone can point me into the right direction for solving it? Many thanks!