Here's a quick fix if you're seeing the following error after upgrading to WordPress 3.3:
Fatal error: Call to undefined function is_rtl() in /wp-includes/general-template.php on line 2102
First of all, don't panic, the error seems to affect the admin dashboard but not the publicly accessible areas of your site. Secondly, it's a fairly simple fix.
The cause is most likely a plugin, and for many people reading this it's the "PopupDomination" plugin.
Fix for "Fatal Error Undefined Function is_rtl()":
- Login to your site via FTP and navigate to the
- If you have PopupDomination installed look at the directory names starting with 'P' and see if you can identify it (it could be "popup-domination", "popupD" or similar).
- Rename that folder to "PopupDomination-broken" or something similar.
- You're done! Reload the page and everything should be working. Contact the plugin author and ask them for a fixed version and re-enable after you've updated.
In the unlikely event that didn't fix your problem, try the following:
- Deactivate all plugins to see if this resolves the problem. If this works, re-activate plugins one by one until you find the problematic plugin(s).
- Try renaming the plugins directory to plugins-broken by FTP (sometimes, an inactive plugin can cause a problem so this works).
- Deactivate plugins in the mu-plugins folder by renaming that directory to mu-plugins-old
You can find more on how to do this on Fixing a Broken WordPress Site
Hope this helps!