Here is a post from some guy on the playstation fourms.
guys and gals,dont worry about the DLC,themes being corrupted. A few months ago I moved house,I had a problem were my system crashed and I couldn't access my PSN games and DLC. What's happened is that because (for whatever reason) your clocks have gone funky,it's basically corrupted the licence that allows you access to the content. You WILL get it back when you next sign in,and update the clock via the internet. To be sure i'm correct,could someone press triangle on a store game and select information,it should (from memory) tell you it has no start date,or that your not the owner of the content. Also check if there is a little star my your user name on the XMB.
It's sounds somewhat correct but at the same time confuses me.