I dont know what the code is offhand, but I know that bosch platinum spark plugs are NO good at all and that they do not work well in our windstars, there have been many complaints with these plugs and windstars, so I would maybe look to change out those plugs with OEM motorcraft platinum sparks plugs. I have heard that autolight platinum spark plugs are good to use too but i have not tried them. I have used NGK iridium and they worked fine for me.
Well I quickly checked up the code and it says EGR insufficient flow, which means your lower EGR ports might be plugged up. Here is a starting point http://leckemby.net/windstar/windstar01.html
Your problem also might be your DPFE sensor, it should be plastic and not metal or aluminum.
If you didnt have the light on before changing your spark plugs then your problem is most likely caused by the bosch plugs or else you disconnected something when changing your plugs.