SpamSentry +-- libs +-- AceEvent-2.0
The directory structure is:
SpamSentry +-- libs\AceEvent-2.0
Which doesn't work so well. This has only happened on the last couple of times I've updated SpamSentry - it was present in both the latest (72774) and the one I downloaded before that (72508).
Curiously, even though the AddOn appears in both the main Blizzard addon list and in the /ace2 list, its not actually in a working state in game.