It may happen sometimes (very seldom it is true) in a WordPress blog that a url (in some “pretty permalinks” type) contains an apostrophe (quote) that causes a 404 error.

Perhaps you found this page, a user sent you a letter complaining for the 404 error, etc., but how do you know if other pages too are suffering from the same issue?

Since quotes and apostrophes may be placed in the url automatically by WordPress, only when the title of a post contains a quote or apostrophe (e.g. in a post like Don’t Care), just search in the titles of your blog to find all those posts that contain an apostrophe, then check which of them (if any) are also published under a problematic permalink.

Enjoy!