In my retail and TOP SECRET RO I have 3 examples of InterfaceArt tex files (texture folder), don't ask me why!
It so happened that I once had an IterfaceArt tex file from one of the Mods slip into the RO system folder, which had me jumping up and down for a while.
There is also a couple or three of "interface" files in the System folder.
Close Steam...
Delete the RO System & Texture folders.
Start Steam, right click on the RO icon in the My Games list/properties/local files/verify integrity of game cache.
Might help, might not.