I've just tried it twice and its doesn't like me first time it told me the date of birth was wrong and had used no nappies and the second time I thought I had double checked it all right its told me no nappies again. Going to give it one more go before I go insane!!
For anyone having getting the "No nappies have been used error".
Could you make sure that for the time periods you have given that:
a) a "total amount of nappies" is selected
b) The "amount of which were dispos" is either not selected or the number is less than the "total amount of nappies"
In theory it should work then. It does for me. Could anyone who is still having a problem forward me the exact information you are trying to enter into the form. It will be very helpful to help diagnose any problem.
I've changed the requirement message on "total nappies used" from "optional" to "required if date selected" to make it clearer.