Scouser helped us a lot with this, hopefully this patch will be worth it.
I was able to get career mode to work. The problem was that some national teams where not set as national teams and had the country set as international. I also made a few other changes, some which may have been needed too for career mode to work.
For the compdata, I added tournaments for the Brazilian and Czech leagues and qualified them to UEFA CL/EL and Copa Libertadores. I also adjusted the leagues which have a different number of teams than in FIFA 16. Career mode will also start in 2010. Some tournaments may need formats changed to match the 10/11 formats and some schedules may need to be adjusted.
By the way, Cork City and Longford Town both only have 15 players, you should increase their squads to at least 18 players.
I would advise you to spend some time testing it before making further improvements or releasing.