This happened without me changing anything except upgrading to 3.2.1 2 weeks ago.
in permalink settings, /blog is hardcoded before the text field for custom structure or category base. This screwed up all my posts across the site. I did not install this under the 'blog' dir, nor does a 'blog' dir exist. I'd prefer a solution without changing the core files.
I previous post with similar title does not answer this question, please to don't to that.
I'm using Multisite option turned on. WP 3.2.1 I recently did a auto upgrade. I backed up the database but not the files >:(
If you are using Multisite version, this is by design that way. please see here. but you may be lucky to remove it. I have recently also tested this, it works in some web server, but does not in others.
follow these steps: