This is a 2.1 Ella "bug":
This is a permalinks issue I believe. I have it turned on, and apparently you can get yourself a 404 error if the title of the article came with a pasted Registered trademark symbol in the title. My guess is this will fail against any odd symbol and it's of course not enough to just delete it from the title and hit save. You have to go to the Post Slug form and remove the offending character.
It might be a good idea to recognize that character type and either ignore it, or rewrite the result to something compatible with a permalink for the typical web user.