I get the same error message. I have only just registered with HMRC for MTD and haven't yet received confirmation from them.

I am trying to submit the VAT return for the period ending 31st March 2019, a period for which there was no MTD requirement. However, I am being taken through the new interface and I assume Quickbooks is trying to make an MTD submission and failing the validation.

Is there a way to make a non-MTD VAT submission for this final non-MTD period?