Under the secure page, there is a link to look up contact information for all teams in the league. This information is updated via the team portal and is the responsibility of the team to keep current.
Stop what you are doing and contact Chris, the system failed somewhere (probably a bad roster entry or bad game id). DO NOT SUBMIT the score until it has been fixed.
Contact the team that is missing the player and ask them to add them to the proper roster. Once the roster has been updated, reload the score system and the missing player will show up.