Looks like you’ve switched from accrual accounting to cash accounting. In accrual accounting VAT is calculated as per the invoice dates, with cash accounting it’s based on the payment date. There is a warning when you switch accounting methods as basically QF locks down invoices in accrual mode not payments, when you switch to cash accounting all those payments from day 1 are unreconciled for VAT so the return tries to pull them forward.
We can solve this for you buy changing the VAT Start Date in the VAT settings area to 03/04/2014 this will prevent any earlier items from getting brought forward.
Otherwise did you intend to switch accounting methods? Switching back to accrual would also solve the problem but you need to stick to the method prescribed to you by HMRC.
Just as I changed the date, it gave me a warning then gave an error, then seemed to work after I clicked save. Should have done a screen snap, I’ve done enough testing in my time!