I had this problem when I first got the Level d 767 and was trying to do the same route. The UNABLE NEXT ALT means that the next waypoint in your FMC has a too high altitude to make it safely. Being that the departure is the LOOP6 the problem is probably the altitude set for LAX VOR. So, to fix this, in the FMC Legs page, next to LAX, write in 1000A. This will tell the plane to cross the LAX VOR at 1000 feet or higher, and assuming that you're on either 25L/R or 24L/R, you will be able to pass that restriction with no problems. Try that and let me know if you need anything clarified or explained. Hope it helps. :) Stephen Anderson