is that something new?
on the front page?
on single posts?
in the archives?
if in some these cases, it could be because of one of the latest posts.
you could try and set them back to draft in the dashboard, and see if this changes something.
it might also help here if you could post a link to your site.
if the your posted code is fully what you have left as sidebar.php – then it is corrupted.
reupload a new copy of sidebar.php.