There is a known issue with the latest version of WordPress 2.6 that means that if you are using SEO (Search Engine Optimisation) friendly permalink urls that include the post name in the url (e.g. http://www.hubbers.com/index.php/a-weekend-in-the-south-of-france/) then viewing individual posts will result in a page not found (also called a 404 page).
The easiest way to fix this is to change your permalink structure back to the default setting so that your urls look something like http://www.hubbers.com/?p=376. But this means that your urls will no longer contain loads of useful keywords that Google and other search engines love.
If you want to keep your SEO friendly urls then I suggest you take one of the following courses of action:
1. Don’t upgrade until they release version 2.6.1 which will contain a fix for this issue.
2. This one is for advance users only. Upgrade to version 2.6 and then go to the following link (http://trac.wordpress.org/changeset/8365) and make the simple edits to the three files shown there. Then upload those files over the top of the ones in the official release.
Personally if I knew what I know now before I upgraded to version 2.6 then I would definitely have waited for version 2.6.1