The NCE 5 amp systems were designed prior to the widespread use of sound equipped locomotives. The higher inrush of current on sound decoders causes the programming track to think that a short circuit is detected. To help eliminate this issue you can modify your command station with this article or add a programming track booster.
Soundtraxx PTB-100 http://www.soundtraxx.com/access/ptb100.php
*** note DO NOT connect a programming track booster of any kind to an NCE Powercab. The programming track mode of the Powercab is a newer design that incorporates the ability to program sound equipped decoders.
Hook up the PTB-100 as follows:
The YELLOW wires connect to the programming track output on the right side of the command station.
The BLACK wires are for system power. The PTB-100 requires 12VAC or 14VDC 500mA. you can use the same power supply that runs your command station / booster PROVIDED that it meets these requirements. A better idea is to use a separate power supply
The ORANGE wires are your new programming track output that go to the programming track.