I believe it is the same problem reported yesterday on this thread, and is caused by some change the AddThis.com made in their sharing widget script that interferes with the NeatHtml anti xss script.
I'm going to investigate this today and see if there is any simple change I can make in the NeatHtml script to solve it.
In the mean time you could disable AddThis from site settings and/or blog settings and I think the problem will stop if AddThis is not on the page.
I can't promise a fix but I will try. I think AddThis has got very aggressive with their scripts. If you inspect the page using web browser dev tools you'll see they are adding all kinds of things to the page, base64 encoded png images, css etc. and they are even manipulating the url to add things there after the page has loaded. I suspect they do this in an attempt to put a tracking code in the url as an alternative to a tracking cookie probably to skirt around the EU cookie laws on a technicality.