How can i fix the flashing door lock light on hotpoint wma13p?

I have changed the door interlock mechanism on my hotpoint wma13p washing machine. The machine allows you to select the programme, extra rinse cycles and then you select start. At this point the machine goes through the motions of confirming my selection and is suppossed to finalise the selection by locking the door, but at this point the door lock light starts flashing and the machine does not start. What is causing this fault?