From BLUE:
The first step in fixing your UI after a patch is to check to see if your favorite addons have been updated to work with the latest patch. This is by far your safest option. Simply move your Interface directory out of the way and install the new versions of your favorite addons.
If there are no new versions of your UI mods, then you can click on the "Addons" button in the lower left of the character selection screen and uncheck the "Check version compatibility" checkbox. This will allow the game to load addons which are out of date, but may still work, at your own risk, of course.
Do NOT run any of the third party tools which renumber the interface versions of the installed files. This is not safe, as you remove the ability for you to know in the game which addons are safely updated and which are still out of date. Not only is this not safe, it's actually more work for you to download and run a third party program than it is to simply uncheck the "Check version compatibility" button in the game.