NEST error message:
IFC01802 - You've already enrolled this member using this enrolment type. If you enrolled this member before and their enrolment status has changed then please choose the appropriate enrolment type and try again.
The member has already been enrolled, so NEST has rejected the duplicate enrolment. However they will still have processed any other enrolments and contributions in this submission, including for this member. You should check on the NEST website, but you may not need to make another submission for this period if all other data has been accepted.
In payroll, please check the Employee's 'Pension Settings' and ensure for the next period that they are set as 'Already in Scheme' so that they are not submitted as an enrolment in the next period too.