The most appropriate course of action when an internal auditor identifies an error that could affect the overall results of the engagement is to inform the engagement supervisor of the error and allow the supervisor to determine the appropriate action to take. This approach ensures that the error is addressed according to the internal audit's standard procedures and maintains the integrity and accuracy of the audit report. References:
IIA Standards on supervision and due professional care, which require that issues identified during audit engagements be escalated appropriately to ensure accurate and reliable audit results.