I am experiencing the same problem but i do not use mytraffic 2013. Is it also an afcad problem?
ALL cases when you have duplicate objects, especially objects from default scenery, are always caused by another AFCAD from another product in conflict. Several AI traffic product might cause this.
Either use the free FSX Airport Scanner program or, if that program can't find anything, you might have to look for a file related in some way to KLAX airport in your FSX folders.
Of course, assuming FSDT KLAX is on top of the Scenery Library, which is where the installer puts it by default. If you moved it manually, anything can happen.