Most likely broken profiles.dat. Open a windows explorer window, type %appdata% in the address bar, go to the Mount&Blade Warband folder and delete the profiles.dat file. You will lose all in-game characters (you just have to create them again using the same names and genders), so if you have some fancy faces you don't want to risk losing, creating a local backup of the file before deleting it might be a good idea.
