An update addressing an issue with the mission "Let There Be Light" where players are unable to complete the objective "Enter Magnys Lighthouse" has been released on PC, PlayStation 3, and Xbox 360.
PlayStation3 and Xbox 360 users can download the update by playing Borderlands 2 while connected to PSN or Xbox LIVE, respectively. PC users can download the update automatically through Steam.
If you're still experiencing this issue after applying the latest update, please open a ticket for additional troubleshooting.