I have an invisible Dialog Tree/Character/etc!
This is a known issue, happens sometimes. Possibly unity bugged out or you deleted a prefab with-out using the powerquest interface.
To fix it, you need to:
1. Select the PowerQuest prefab (from Tools menu)
2. Change inspector to "Debug" mode
3. Scroll down to Character Prefabs/Dialog Tree Prefabs and remove the empty one, or drag in the correct prefab.
4. Then change the inspector back to Normal mode.
