Completely in the same boat as you man, I've started a Steam ticket but there seems to be no official or unofficial response/fix anywhere. Really sucks.
As Sekij said, Napoleonic Wars works, but Native on Warband just has seizures and treats me as if I pirated the game, I started a Steam ticket about it but no progress yet, and yes it happens with all Servers.
Alright so I just bought M&B on Steam during the weekend sale and I've been trying to play Native, however I've been getting kicked anywhere between 30 seconds - 20 minutes into the game, all other support forum posts I've seen are of blatant pirates but my serial key is one given by Steam. I...