I have the same problem. When I initially downloaded the program, it ran fine. Then I installed FSPassenger and then the addons option in fsx disappeared. I had to un install everything that ran through the addon menu reinstall FSPassenger then install the FSDT products and plus the others that ran through the addon menu (LDS PMDG, etc)
Ever since, the KDFW hasn't been working properly, I have about 4 terminals missing plus other buildings around the field. I have tried pretty much everything already mentioned above, without succes. Whats puzzling me though is that all the other products I have from FSDT/Cloud9 works. (KMCO,KFLL,KJFK,KORD)