You are generating the IRP5/IT3a report or printing the IRP5 Validation report and the following error appears:

It is possible that there is a negative value which has been captured on the employee's Add Tax deduction line.

It is possible that there is an amount which has been captured on the Additional Tax line (with IRP5 code 4102) as a negative.

Print the 12 month or History screen report to check this.

Employees cannot have negative values on Additional Tax.

This must be removed in order to proceed with the IRP5 run.