I don't have an answer for you, other than something on your system is killing VA's keyboard hook. VA is unaware that the hook has been broken (it just stops receiving notification that keys are being pressed).
Since although it's not completely uncommon that this occurs, it's one of those things where there is an outside influence causing an issue in which VA is unable to recover (for instance, I'm unable to reproduce the problem here, even after several hours of WoW). Given that, what I'm looking at doing is seeing if there is a way to detect if and when this happens and then look to see if there is a clean, unobtrusive way to reestablish the hook.
Again, I don't have an ETA for you, unfortunately.