I've just encountered this issue, & after much searching online, it appears that it hasn't been resolved at all.
I bought the DLC over a week ago & still haven't been able to get it to work. I'm in the UK, so have access to the EU PSN store, which is where I got the DLC from, & my disc is EU as well... BLES-01161 (which is the Limited Edition) Why has this issue not been resolved yet? I've paid for something & there's no reason why it shouldn't work. Answers from Obsidian?