Andrew Yoon of PS3Fanboy says,
"The Rock Band forums are being torched down by angry PS3 owners that downloaded this week's PAX Pack DLC. According to every single post on the forums, the $3 pack simply doesn't work. 'I just downloaded the PAX pack on my PS3 and I can't play the songs,' one user notes. 'They all show up in my setlists in the game, but everytime I select one of them to play it goes to the loading screen and gets 'stuck.'
Harmonix hasn't issued a comment yet about the cause of this problem, and an approximate ETA for a fix. We're surprised that such a damaged download pack could go live -- don't they usually test these things?"
Those that have downloaded the Pax Pack are having the issues, and there are also issues with the MC Frontalot individual track, "Living at the Corner of Dude and Catastrophe." The other two individual tracks are working properly. HMX Alex, a dev on the Rock Band forums posted this last night,
"I have reported this issue to the proper authorities. Will update when resolution is provided."
HMXHenry just added this in the Tech Support sub forum,
"Hey gang. We're working with audio to get to the bottom of this. It appears this issue is only tied to the MC Frontalot track, so the other two tracks from the PAX pack should be fine solo.
As we sort things out we'll post more info and a solution for those affected."
UPDATE 2: According to the Rock Band Forums, the song has been fixed. Simply re-download the song, and it works just fine.