Strange that as its only when I go the team that I initially had the problem. If I didn't go the full team I couldn't create the issue you had, however I just did the windows and the skin name so they were different names and not a problem.
Ok I created a team and everything works as intended so files and naming must be correct, but still can't get it to work properly if just trying to add skin to base car for sharing in league race.
I too had the greyed out windows when creating the team but after adding the window files and selecting the team everything was correct.
And I know it's just not my system because I am trying to solve this for another league member that is having the same problem plus the guy that started this thread.
What could possibly be different by adding the team?