my question is regarding hotpoint aquarious extra WMA34, 1000 spin?

When I put clothes into my washing machine (Hotpoint Aquarius Extra WMA34 1000 SPIN), I lock the door and select the appropriate program. It starts working fine, however after some time, during the washing period, the light starts to flash, indicating that the door is not locked. I try to press the door inwards, but it doesn't work. I then, open the door and close it again; it doesn't work. The door light still flashes, showing that the door hasn't locked. I even try to move any clothes out of the door way, when i open it but it usually makes no difference. How can I rectify this problem?