How do I input the serial key for multiplayer?

I've owned Napoleonic Wars as well as Warband and With Fire&Sword for about 80 years now and they are listed under my accounts "games".  The serial key is blocked with the exception of the last two letters for each game.  If I remember correctly I've always copied and pasted this serial key into the game when asked and it's worked (mostly for warband).  In this case I've taken interest in trying the Napoleonic multiplayer again (it's been years), after I clicked a server it ask me for my serial key.  I can't paste the serial key which I've copied from my account/games, in fact I cannot paste anything into the space for the serial key.  How am I to input the serial key if I cannot read or paste it?  Surely I'm missing something.  Thanks for any reply.

i was entering the wrong password for "showgames"

If you struggle entering your key directly into the game, you can do it through the Windows registry base.

[list type=decimal]
[*]Do ALT + R, a box 'Execute' or something of the sort should open
[*]Input 'regedit.exe' and press [ENTER]
[*]Go to HKEY_CURRENT_USER/Software/MountAndBladeWarbandKeys
[*]Change the content of "serial_key_nw" for you Serial Key
[*]If it does not exist: Right Click → New → String Value → Name it "serial_key_nw" → Double click and enter your CD Key.
[*]Try to connect to a server
[/list]