Upgrading to WordPress 3.1 was a complete disaster for me. It became very hard to update my blog, because the following things happened:
- The visual editor broke, and HTML would show up when it was selected.
- I couldn’t insert media into posts… the Upload/Insert buttons were all broken. The only way to insert media into my posts was to manually add HTML.
- It became impossible to set categories or add tags to posts.
I found a troubleshooting master list. Everyone says to start by disabling plug-ins. I was skeptical, and didn’t do that at first, but after trying a bunch of other things to no avail, such as reinstalling WordPress 3.1 and fiddling with file access privileges on my server, I finally gave in. D’oh! As soon as all plug-ins were disabled, everything miraculously started working! After re-enabling the plug-ins one by one, I isolated the culprit – it’s the WP-Stats-Dashboard. Its page claims it’s “Compatible up to: 3.1.” Don’t believe it. As of v18.104.22.168, it still breaks WordPress 3.1.
Update 2011-04-23: As of Version 2.6.1, it’s OK to use WP-Stats-Dashboard again.