I had almost the same problems.
Try to do this:
Removed the game data file on the PS3 (less then 100k). Then I started the game and went straight to the 'in Game store' and to the Mappack. (that was not possible before when I had installed the SeasonPass...(Before I only got a error msg)
Notice: (Do NOT download the seasonpass again before you do this).
voilá.. the IN GAME store works for me.
:-)