Same trouble as Anguish.
As I keep getting C++ Runtime Errors I downloaded the 1.34 version of the game from the website to give a fresh install a try rather than going through Steam, to see if that was my problem. My original key, which is a 5x5 on the back of my M&B:WB manual, is 'Invalid' and after putting it in a few times it now says 'IP Banned'...which is hardly helpful. Is my 5x5 solely tied down to Steam only? If it is thats a wee bit silly in my opinion especially if I wanted to play it on my laptop upon which I do not have, nor want to install, Steam on.
EDIT: Downloaded M&B:WB from Steam & got my 4x4 key from there.