Yeah, the interface files probably changed since the last release of my pack (which is for 1.28), so it could well be the cause of your problem. You should restore all files in the \Resources\Interface\ folder to those from whatever version you're running.
Actually, there's really no need for this pack now since 1.29 includes basically all of the graphics from my last pack, and everything important will be included in 1.30 when it comes out.