There can be three different causes:
1. The brew group / coffee grounds has not been inserted
Make sure that all components have been inserted and closed correctly. Make sure the brew group is set in the correct position before placing it back.
2. The service door is open
Make sure that the service door is closed correctly.
3. The control dial is not in the correct position for machine operation
Make sure that the control dial is in the correct position for the required action.