STOP right there !!!
go no further !
before you Jump the Gun - Tell us all something , have you downloaded another scenery / airport and installed it in your flight simulator

?
and do YOU know for a "FACT",,,,, that it DID NOT have a FS/2004 A.I. Flight Plan in there
Because if sim pilots try to inject A.I. Traffic Plans / Files from FS/2004 into FSX of any version - you'll permanently ground all Air Traffic in FSX !!!
That's the 1st thing you need to make sure of - because if you don't - you'll re-install or repair you sim and STILL have NO A.I. Traffic , until you get rid of those FS/2004 A.I. Traffic file / plans !
Another Discussion Recently on the same subject :
http://forums.simviation.com/phpBB3/viewtopic.php?f=19&t=170932&p=1266598#p1266598 "Don't Mix FS9 and FSX Traffic Files: !!!!
FS9 traffic files are compatible with FSX. However, as described more fully in the User Manual, if FSX "sees" a compiled-for-FS9 traffic file, it will generate AI traffic for that file and any other compiled-for-FS9 traffic files it "sees"; but, it will "NOT" generate traffic for any compiled-for-FSX files. This has nothing to do with AI Flight Planner. It is a FSX "feature".
So, if you "DON'T" get (or suddenly stop getting) AI traffic from compiled-for-FSX traffic files, the first thing to look for is a compiled-for "FS9 file" somewhere within FSX's scope - probably in the Scenery\World\Scenery folder. You'll find AI Flight Planner's Find FS9 Files function very useful for this.