I just enountered the same thing:
Message 8 of thread of forum Faith and Belief does not exist. Please click your back button and try again.
It happened on another thread a few minutes ago too, but by clicking on the page instaed of the post, and then refreshing the page, I was able to bring up the new post that had originally been declared not to exist. Didn't work this time.
Edited by Faith, : No reason given.