What this means: Two or more records share the same employee identifier. Jarvis needs each to be unique.
Why this might happen: Similar to E020: either the export includes duplicate rows, or two workers have been assigned the same ID.
What to do
Follow the same approach as E020, but check the employee ID field instead (EmployeeId in PAPDIS, Alternative Unique Identifier in NEST, PAYROLLNO in NOW:Pensions, Worker Ref in Access Pay & Bill).