I am also getting this error on random posts. None of the above suggestiosn apply to me, so maybe I should just reinstall everything. Using 2.6.1. With some posts I just deleted them and created another identical one, but once a post collects comments I am pretty sure that the comments would all go bye bye too if I deleted. I’ll add here, in case it helps anyone think this through, that I had the same problem on my wamp server and it persisted through the port to the online server. So it is probably not a server-specific problem? (I shouldn’t speculate, since I don’t really know). Also, I think I might be able to connect the error to posts that were created before system-wide configuration of some sort, for example activating SEO friendly links.