I am having trouble compiling traffic at major airports. It works perfectly at small airports, like Cedar Rapids (KCID). However, regardless of what I do, I have trouble at the large airports, like LAX or Newark. I will compile the flight plan, but when I go to the airport, the added specified traffic never appears. Could somebody please advise me on what to do?

I have been using AI Flight Planner (freeware at http://stuff4fs.com/open.asp?Folder=AIFP&JS=TRUE). It will tell me if there are errors in my flight plans, and even then some of them don't work completely.
Sounds like this is the trouble you are having (not with having the right compiler). Even with software that does a lot of the work and running the numbers for me I just have to keep going in and check each flight plan and leave enough space (time) for the legs to work.