Hi Tim,
Without seeing your log.txt, I don't really have enough information to look into this more, but here are some general tips:
First I would check to make sure you have planes selected in the Aircraft & Situations screen for the air drop (it's the third line & last line under "other aircraft profiles.")
If that isn't the issue, try moving the preferences folder to the desktop. Next time you start it will restore the defaults and you can check if that fixes it.