How can I fix my indesit idl530 with a blocked filter alarm?

Hi - I've got a Indesit IDL 530 and the blocked filter alarm as it said in the manual keep flashing (first and third lights) I've taken the filter in the bottom to pieces and cleaned it and used one of those dishwasher cleaners but nothing seems to work. The program seems to start fine but when it gets to the rinse cycle (3rd light) thats when the lights start flashing and everything comes out gritty and cloudy - any ideas would be greatly appreciated.