I just ran into this issue as well, two days in a row, using the paid, hosted https://write.as version of WriteFreely, so it seems to still be an unsolved bug.
I have an anonymous post in draft and when I try to preview it I get the status message Generating... but nothing happens. If I publish the post I get the errors Failed to post. Please try again. (404) or Failed to post. Please try again. (0). Also, the page https://write.as/me/c/USERNAME/stats sometimes loads with no CSS.