Not being able to see your site, since it is private, I will have to guess that this is caused by an HTML error somewhere in a post.
Go to settings > writing and check "WordPress should correct invalidly nested XHTML automatically" and save. Now open your latest post, make one minor change such as adding a space and then deleting it and then click update and check your site again. If all is well, you are golden. If not, open the previous post and do the same thing. Continue with this till you find the post with the error. The change at settings > writing will get WordPress to automatically correct any HTML errors in your posts.
If that doesn't work, we'll have to be able to see your site, so you will have to make it public for a short time so we can look.