We are currently investigating this issue but, until we are able to deploy a permanent fix, taking the following steps should allow you to workaround the problem:

1) Go to the customisation menu before loading My Team

2) Change any 'official' liveries (cars, suits etc) that you can't customise (70th Aniversary, Racenet, WeRaceAsOne etc) to one of the basic liveries

3) Choose to use these liveries in the My Team mode.

You should now be able to play the My Team mode again.