I am unable to get the Database build to start. It cuts out immediately.
I have got FSX running on an external drive using a USB 3.0 connection

Answering my own question, I have found that if the leg on the Flight Plan is highlighted prior to the actual leg you are flying, the system will eventually synchronize itself.

I have come up against a small problem when opening up a saved flight with Plan-G. The Active leg on the Flight Plan lags behind the actual leg.
Is there a way of synchronizing the Flight Plan and the leg that is being flown? The GPS also reflects the unsynchronized legs.
Everything is in synchronization until returning to the flight at another time.
Right clicking the Flight Plan leg to try to correct the sync is not successful.

Having downloaded two "Tile Files" into the DEM folder and created a Flight Plan, the "Plan Elevation" box remains 'grayed out'.