The brew unit is not positioned correctly.
Make sure that the handle is positioned correctly.
Press the button on the bottom of the brew unit handle (1). Whilst doing so, turn the handle forwards (2).
Slide the brew unit to the side into the coffee machine as far as it will go until the brew unit is right up against the housing panel and the drive.
Press the button on the bottom of the brew unit handle (1). Whilst doing so, turn the handle backwards (2).