I have membership installed and it has worked fine until my

I have membership installed and it has worked fine until my recent attempt to block portions of posts (I only do on a few posts and they are usually a week or so apart in time).

I am using the [level-premium] to block (and unblock). The message that you must be a premium member to view additional content shows up, but so does the rest of the post.

I have recently been making some changes to advertising providers (added Kontera, Chitika, Bidvertiser and B4ps). I also recently added Zemanta. I suspect one of these changes has caused the problem.

What must I do?