dash lights?

have just changed fuel filter on my 02 diesel trafic was dificult to start after new filter then started n run a minute then stopped took ages to start then run for a minute then stopped this happend a few times then put old filter back in it started straight away and runs fine ticksover revs up holds steady revs BUT the red STOP light stays on and the red ENGINE light continually flashes ????? any ideas please

paul
April 2010