OK, I just got to the part in the citadel where all of your weapons are confiscated except the super charged gravity gun. I killed all the badguys in the area. The problem is that I can't open up any of those damn forcefields. Each path is blocked except one that has a fence at the end that leads into a big room where I can see that large enegry beam but for some reason(a bug?) at this point of the game my ability to jump seems to be disabled. I read two FAQs telling me to use the enegry cores from that large beam. I pointed the gravity gun towards that large beam while standing on that balcony but nothing happens. =(