I've been trying to find the answer to this problem for weeks with no luck. Every time a friend of mine and I try to play BL2 together from the same LAN ends in failure. It doesn't seem to matter if we're signed into PSN or not.
Every time, the game brings the connection screen, establishes the connection, but then kicks us out back to the starting lobby with no error message.
We've tried changing the network settings to LAN, signing out of PSN, putting each PS3 on a different router in the same network, and connecting them directly with a crossover. On each configuration, we can each see the other player in the active roster from our individual lobby, so I know the two PS3s are communicating.
As far as I know this should be working, are there additional setup steps I'm missing?