Hi gabrown,
Looks like you just made it to the Master Tier in the last few rounds. Congrats on that!
The reason you are seeing that message is because you entered the tournament you were trying to play as a Pro Tier player. You remain to compete in the Pro tier for the duration of the tournament, so you can't use your Master Tier clubs for that event. Any events you enter after turning Master (or for any regular rounds you play from this point forward) will allow you to use your new Master clubs.