Well... FSX has been deleted from my system since october 2014, but see following questions...
Depending of the version of your "regular FSX", you might have a SDK, possibly containing the Traffic Toolbox thingie. When yes, install it into your FSX.
I do not use Steam at all, so can not tell about it.
Does your AIFP main window show the correct simulator TARGET VERSION?
When you are creating a flightplan, do you validate it (select Flight Plans, then validate)?
If the file validates, then there is normally no mistake into the flightplan itself, all necessary components (airports, aircrafts) are there.
To which directory are you compiling the traffic file, or move the compiled .bgl file?
Should be something like FSX\Scenery\World\scenery\...
How do you check how the AI traffic displays into your simulator? Check that your aircraft is at the right airport at the right time of the day (local time, or UTC?) to see a departing, or arriving AI flight.
Do the airports you are using into your flight plan contain appropriate, and sufficient, parking spots for your AI traffic?
No parking place = no place from which an AI flight can start, or when arriving, the aircraft lands, but then disappears as there is no place it can go to park.
The above being checked, will certainly allow the techies and gurus to provide useful suggestions or advices...
Blue skies