When you sync, you will need to match up EVERY bowler to what is in the DB already.
If you cleared the MBD and linked your first league, it should be fine without that message because no one is in the DB. But each time you link another league, you have to walk through each bowler to tell BLS/MBD to use the bowler in the MBD or to add that bowler in BLS as a new bowler in case it's a different person than what is in the MBD.
CDE Software Staff
Remember to always make sure you've downloaded and installed the most current update to see if issues experienced have been corrected.