I keep getting a 404 Error when trying to preview, save draft or publish new post. I have tried this with all plugins disabled - same result. I notice that the draft actually does get saved, but I found that by clicking on the Posts link. When opening those drafts and trying to preview them the result is 404.
So I keep trying to add this as a new post. I delete the previously saved drafts. I also notice that sometimes when adding the title the post is saved and a permalink is generated - the proper permalink that matches my settings. But sometimes the draft isn't auto-saved and the permalink is not generated, at least not visibly. This is a random symptom.
I am running 3.1.1 (current version) and Thesis 1.8, all plugins and theme completely upgraded.
I tried just putting the title in and previewing - that worked okay, but when I added my content (copied and pasted from Notepad++) which is only 200 words long, the save and preview and publish return the 404 error again.
So I tried this AGAIN with the default and the Twenty-Ten theme - same results.
It turns out this same issue happens with pages as well.