The multi-team player file has a maximum amount of transactions it can hold. This limit is rarely if ever exceeded by actual in-season trades. Very often, when you create a league you might have failed to restart the league before you began play and many of the 75 transactions took place setting up your rosters before the season began.
Unfortunately, there is no way around this maximum limit in solitaire leagues. In multi-player leagues, you can use the Rebuild League function if you have all of your game results files saved.