ddman,
I think the door control command may be an add-on as I've never seen it in 3+ years of using TRS2006.
juveboy640,
If you're using the built-in HST and carriages, then the doors will not open. However, if is an add-on, then they should open every time you pull up to a station.
Next time you test it, pull up to a station. If the DCC controls (if you are using them) vanish, or if the cab levers stop working, then the train is loading. After control has been returned, hod CTRL and right-click on a carriage to see if there are any passengers in there. If there are, then there is no problem with the type of passengers. If not, then there is a problem other than the train.
Sorry if any of this is obvious,