Last thing I heard was that there was a change in AceEvent causing a lot of addons to go nuts out of no reason.
E.g. ItemRack stopped doing anything but I did not update it for some weeks.
The major problem was that there was some old version of AceEvent loaded which bugged pretty much the whole interface.
Nymbia posted a solution for the situation (e.g. either running without externals or updating all copies of AceEvent) in several threads at the wowace.com forums.
This thread pretty much sums it up. It also includes a link on how to use Ace mods without externals.