Since I updated Wordpress from 3.6 to 3.7, I'm not able to visit the single-pages on my custom post types, then I get a 404 error. I thought this would be a rewrite_rules issue, so I've tried the following:

-Go to the Permalink settings, click save (flush rewrites)

-Manually deleted the rewrite_rules from the option table in the DB (I was desparate, and it seriously worked for me one time)

-Re-check my .htaccess, but this is the exactly same as instructed on the permalink page

-switched off the plugins

I also tried switching the permalink to the "ugly" url (eg. ?page=35) and check if the articles worked, and they did! So I'm pretty sure it's a permalink issue.

Now I rolled back to 3.6 again, but I of course want to upgrade in the near future (security etc.).

A remarkable thing was that during the rollback I checked out a single page (notice that I didn't rolled back the database yet, only the files) and surprisingly they worked again.

Any suggestions on how to solve this?