This is because the Competition site concerned operates the play-cricket League player registration option, which requires clubs to submit details of their players to the Competition for registration, and which allows only players registered via the system to be included in teams for League matches. This over-rides the squads entered absolutely.
All participating teams should have been made aware of this; if you have not then you should contact them regarding this as they may have activated the option without being aware of its implications. See the League Registration help guide here for details of how to register players with a league that requires this.
If you are required to register your players for the league online, then go to Admin>Members>Member Database. Click on the Edit Roles icon by the players you wish to register and find the League Registered Players tab, update the details there with those required by the league, click the Save button, and then the 'Apply' link to the right of the tab before using the 'back' button at the top to return to the list. You will then have to wait for the league administrator to approve them before you are able to add them to teams and scorecards