What kind of 9V battery are you using? A standard block battery? That probably don't provide enough current for the motors. Please provide links to the motors you connected to the shield. And if you use another battery, provide a link to it.
What kind of 9V battery are you using? A standard block battery? That probably don't provide enough current for the motors. Please provide links to the motors you connected to the shield. And if you use another battery, provide a link to it.