If I come to a stop during taxi and then advance the throttles there is no movement, I have to apply and release the parking brake to get going again.

The parking brake lever is in the released position with the red light off,

Any Ideas?

Nothing to do with the NGX buddy. That is your simulator or your controls. Check it with other aircraft and see if something is binded to your throttle. I have the Logitech G940, and it is a dual throttle set up. Check your axis' set ups and see what is set to what.

I have had this problem for years with various aircraft. For me it only occurs if I use differential braking, then I have to tap the period key to clear it when I want to start moving again. 

 

It almost seems like a bug in FSX or something. I use the CH Pedals what are you using?

I also use CH Pedals and Yoke with the recent addition of a Go Flight TQ6 Trottle quadrant.

 

I am just in the process of setting up the Super 80 to test that. I seems ok using the throttle on the Yoke but have not tried the Go Flight throttle yet.

Ok. So this problem does not occur using The Flight 1 MD80 and with either the CH Throttle or the Go Flight TQ6 Throttle.

Found the problem. FSX had allocated default joystick assignments without my knowledge when I installed my TQ6 throttle. These were interfering with the assignments made in FSUIPC.

 

The solution? Delete the fsx assignments.

Nothing to do with the NGX buddy. That is your simulator or your controls. Check it with other aircraft and see if something is binded to your throttle. I have the Logitech G940, and it is a dual throttle set up. Check your axis' set ups and see what is set to what.