"Disc Unreadable" Error Solution (Kind of)

I'm interested to see if anyone else has experienced this issue.

I was playing co-op with my friend the other day and he decided to load in his Mechromancer. I didn't have the DLC at the time but I did have the compatibility pack installed.Every time he loaded in his character I would get a "Disc Unreadable" error. Finally, I caved and bought the new DLC and then everything was peachy.

Shouldn't the compatibility pack cover that stuff?