Some of my users are seeing this error message coming up periodically when posting / editing a post. I’ve not seen the error myself, but I think this has only started after I updated to the latest beta (v1.8.0.beta4 +4).
There’s a thread here on it: Weird error when posting or editing - Site Feedback - Audio Abattoir
It doesn’t seem to be actually blocking functionality (you can still post if you just press OK on the error message etc.) but thought it worth mentioning.