Post what addons you've updated recently.
You can actually most likely figure it out on your own if no one knows off the top of their head. All you do is go out to the Character Select screen, go to the AddOn button, go in and disable 1/2 of your addons, the log back in. If it shows up, it's one of the ones in that group. If it doesn't show up, it's in the group you disabled. So, repeat again with whichever group has it in it. Split the group in half, see if it shows up. It'll whittle your addons down pretty quickly, give us an idea of which one (or combination of ones) is causing it.