The 1.174 update for Warband (which pairs with Viking Conquest version 2.044) was critical for modern compatibility. It addressed:

: Using keys found on public documents or "key list" sites often leads to "Activation Denied" errors, as those keys are frequently blacklisted or already in use by other players. Open - Key activacion | TaleWorlds Forums

: Some newer 4x4 keys may not authenticate correctly with much older versions of the game, though 1.174 is generally compatible with modern keys.