Here are some suggestions regarding this issue.
On your PS3 please double check the other account users and also thy with a new user.
This solution worked for this player (Skate forums)
However the most probable cause of this issue is the region locking.
For users who are unable to access their DLC, it could likely be due to the PS3 region locking downloadable content.
What this means is that players who purchase DLC from a different region than that of their Game Disc will be unable to access their DLC from within the game.
Here are the details: