Can't access to my DLC-cars...

EDIT: erase this post. the issue solved for now. Will probably return again because this was the second or third time I was unable to access my DLC cars…

For future reference regarding DLC, you may want to check the FM5 FAQ: http://forums.forzamotorsport.net/turn10_postsm67056_Forza-Motorsport-5---Game-FAQ.aspx#post_67056