I have an unpatched version of FIFA07 at the moment. I used CM 07 to add in White Hart Lane off of ECP and it worked fine. However, when I changed tournament names like FA Cup and UEFA Champions League, etc etc, and save, I open up FIFA 07 and all of the sudden not one single player shows up on team lists and, subsequently, I can't play. Any ideas on how to fix this?

go to team management and select "Reset My Squads"

this should fix it.