Bought Mount and Blade Warband for Steam, but will not let me put in codes &...

[Lastonestanding]

Hello I just bought Mount and Blade Warband for Steam, but will not let me put in the it is asking for codes & and it will not let me play Multiplayer with my friend! Here is what it is telling me every time I load the game. Please let me know what is up Thank you~ :

image with personal data removed

 

[MArdA TaleWorlds]

Steam should not ask for any serial keys. Are you using a modification?