Does it still happen when you disable ALL addons? If so, it's not related to addons, but a bug in the game itself.
Otherwise I suggest you install
LibDebugLogger if you don't have it yet. After you have it installed and got the error, log out of your character, go to your
Saved Variables folder and upload the LibDebugLogger.lua
somewhere, so you can share it here. That might give a clue why this error is happening.