Sorry Den typo, I meant National Insurance Number, it is this number that DVLA required. Correct number was entered but rejected. This from DVLA instructions

You’ll need:

your UK passport (either current or expired within the past 12 months) or the document you used to set up your online immigration status
your current driving licence (if you have it)
your National Insurance number (if you know it)
addresses of where you’ve lived over the last 3 years