Update - Just for grins I started a new game and have been playing it here and there. On the new game I can get the steward to talk to me and it opens up the White March expansion normally however, if I load up my original character I still cannot interact with him/it at all. It must be some sort of condition that you triggered in the game. My thought would be when you took over the keep and had the option to let the crazy guy's soul (sorry I don't remember his name) go, stay, etc...
One the one that is broke I opted to have his soul stay in the keep as a guardian. i.e. the steward.
On the game that works I released his soul and the steward has a female voice and 'works'.
Anyway, that's my running theory.