BetcoinPoker.com has two types of tournaments:
1. Betcoin only tournaments which are in mbtc
2. Shared tournaments with the WPN which are in USD
When you create an account on BetcoinPoker.com, it is a unique account in the BetcoinPoker.com database, however when you play shared tourneys you will need to create another username because 99% of the time your current username is taken most often by you when you signed up for AmericasCardroom.eu, BlackchipPoker or any other website on the Winning Poker Network. It is also highly likely that it is taken by someone else.
Therefore you need to create another username. Typically players add a 1 or _ after their Betcoin username.