edit: for me, this seems to be tracing to a very old addon:
CCWatcher. disabling this addon clears the problem.
current versions of Ace2:
AceConsole-2.0: 91094
AceTab-2.0: 91098
CCWatcher versions of Ace2:
AceConsole-2.0: 48940
AceTab-2.0: 40685
in my case, some of these CCWatcher libraries are loading early, and all my other Ace2 addons are then trying to use them. enabling an external copy of Ace2 overrides all of this, and also seems to clear the problem (and CCWatcher seems to operate correctly on the latest/greatest Ace2).
i expect you have something running around loose that embeds an "old" version of Ace2.
-----
one of my users reported this. the error was tracking through the version of AceConsole-2.0 loaded by Aloft.
i did not see this originally, yesterday, but i am seeing it now (i just updated a bunch of addons). it happens with the latest (WoW 3.3) version of Aloft disabled. i am working on isolating it now. will follow up in a bit.