So your shield works 100% on a Uno and Mega running the library examples.
If you have a problem with your own code, please post your sketch and a schematic of your wiring.
A simple pencil drawing of your wiring is fine if you attach a good photo.
A written description of your wiring is fine too. But check it VERY carefully. The description in your message#13 is not accurate enough. Put yourself in our shoes. We do not know whether you have connected GND wires, what kind of power supply, what pins are connected ...
David.