I'm having a same kind of problem that Riddle so I decided to describe my problem here instead of making a new topic.
I bought Mount&Blade Complete from Steam a week ago. It contained the Vanilla Mount&Blade and Mount&Blade: Warband. We have three computers on our household and since my brother has been playing this game quite some time I decided it would be easier to copy the game(s) from his computer to my external hard-drive where i have my Steam-folder and the verify them. Everything went smoothly with Mount&Blade and I was able to play the game the same evening I bought it but Warband had problems. After I verified the game files Steam it started downloading some fragmentationed (I hope this is the right term) files but then stopped downloading the game at 99%. When I then tried to launch the game it said "The game is currently unavailable. Please try again at another time" or something like that. I was pissed and decided to play Mount&Blade and suspend the problem at another time.
Couple of days later I tried again and still the game said the same thing. I then Decided to delete local files and download the game files via Steam servers with no result as the download again stopped at 99%. the weirdest part is that my brother has been playing this game almost daily with no problems and also my other younger brother, who decided to buy the game at the same time than me since it was 50%-off, has been able to play the game without problems!