This is a glitch I've noticed in Carb that you may also be seeing if you have Carb set to show/track Achievements. When this happens to me, I cannot click, move, minimize, or do anything with Blizzards Objectives Frame.
The scenario is:
1. You are using the Carb Quest Tracker.
2. You have manually chosen to Track certain Achievements through the Achievement Window. Which then places them inside the Carb Quest Tracker.
3. You have at some point minimized the Carb Quest Tracker and logged out *with the Quest Tracker still minimized*.
The end result:
You log back into that toon, the Carb Tracker is still minimized, but now the Blizz Objectives Frame shows the Achievement. And now you cannot do anything with the window.
The Fix (for me at least):
All that's needed is to Maximize then re minimize the Carb Tracker. Carb will grab the Achievement/s you are tracking and place them back in it's own window, then re hide the Blizz Achievement Frame.
Hope this helps