When you submit an EC sales list, if there are any errors on it this doesn't become apparent until you get an email from HMRC that there was a problem. You then can't resubmit the EC sales list after you have corrected the error. Could I suggest one of the following:
(1) A submit button for EC Sales list so you can submit these separately if required
or (2) the ability to validate the EC sales list first to check that there are no errors before you submit the VAT return (to which it is attached)