How do you change yor rosters in MLB 2009 The Show?

Every time I tried to change it it saids all CPU Rosters must be VailedHow do you change yor rosters in MLB 2009 The Show?You can call up, send down, trade, or sign free agents but you have to make sure that there are 25 players on your active roster. Than is it still says computer rosters must be valid select auto management.