While submitting your SA100 returns, the HMRC (Government Gateway) is returning the following validation message:
Error Number: 6791
Error Location: /hd:GovTalkMessage[1] /hd:Body[1] /MTR:IRenvelope[1]/ MTR:MTR[1]
Error Type: business
This message suggest that you are attempting to submit a return for a Tax payer who is
65 years or older. You may have an Income entry that results to Class 4 NIC calculation but have not ticked other relevant boxes.
HMRC server suggests there must be an entry in one of the following field (only in the form you have selected):