Your attempt to edit this post: "title" has failed
is the result after trying to Save a trivial post of title + paste some text into the post body. The title is saved, but not the body of the post.
I often do this to save a quote or URL for authoring a post later. If nothing else, having this simple test scenario work is essential for people to have confidence in WP.
ENV: Trunk / r7641 (2.6-bleeding)
Firefox/3.0b5
ADDITIONAL DETAILS
My guess is that it's a timing issue related to the trigger of the first autosave.
The please try again link is to 'wp-admin/post-new.php' which also doesn't inspire confidence.
I searched and there are a number of discussions on the forums with this error message. http://wordpress.org/support/topic/165717 includes the most insights and seems to suggest that there may be 3 possible issues here: conflict with plugins, byte order mark, or conflict with autosave.