There's a tool somewhere to check you haven't got any FS9 traffic files - if you have, they kill ALL aircraft traffic files. Might be worth looking at, especially if you've installed anything with traffic recently?
EDIT: http://stuff4fs.com/open.asp?Folder=AIFP&JS=TRUE
that's the link to AI Flight Planner, which has the tool I mentioned for checking for FS9 traffic files in FSX