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?