Not sure exactly what it might be without seeing it, but few ideas: did any of your players get injured in the first game, but are still in the rotation? Did you sign/cut any players in a way that affects the roster limit?
If you can't identify the issue from the error message or looking at your roster/rotation, you can drop a support ticket and include the game file in case it's an internal file issue:
https://wolverinestudios.freshdesk.com/ ... ickets/new