I recently upgraded to WordPress v2.6. After a quick check, everything seemed to work fine. However a few minutes ago a reader of this blog told me that he encountered some problems: The overview would work, but everything else like reading certain posts, commenting or using the RSS feed produces a “404 – not found” error. I quickly found out that the blog was experiencing bug #7306. The suggested workaround, filling the category and tag fields under wp-admin -> Settings -> Permalink, worked instantly and now everything should be up and running again. Let’s hope WordPress v2.6.1 will be released soon to fix the problem without the need for workarounds.
Yep. I ran into the same problem (http://danny.damours.net/wordpress/index.php/archive/wordpress-26-released).
Frustrating. Especially because I didn’t find out for a day that my posts were broken. Also adding in category and tag fields changed my permalinks for those pages and so Google kept trying to crawl the old URLs for those.
It all seems fine now.