I2C Motor Driver with Pololu stepper motor

I have a V1.3b version of the motor driver and I’m able to Control the stepper directly by Arduino.

However, I’m unable to Control the Stepper using the I2C motor Driver V1.3 on-chip Atmega8L. I have used a logic analyser and I can observe Stepernu and EanableStepper messages being transferred and acknowledged. The red and green leds for both sides of the board remain lit, but the motor does nothing.

Any ideas?

David