Please update your addons

[WOWVern]

Sounds simplistic enough. Let me clarify:

Some addons are causing WoW to crash in the loading screen with "Load Out of Date Addons" checked. I believe Blizzard has made it mandatory (due to the Background Downloader being run) to have as many addons up to date as possible. It means more work, but in the long run it makes the game run smoother.