Since the below query displays errors at the line level, the join between "AP_INVOICE_LINES_INTERFACE aili" and :AP_INTERFACE_REJECTIONS air" should be via "invoice_line_id" rather than "invoice_id" in order to point out an acurate error.

Select aii.Invoice_num , air.PARENT_TABLE, air.REJECT_LOOKUP_CODE, air.parent_id
From apps. AP_INTERFACE_REJECTIONS air,
apps. AP_INVOICE_LINES_INTERFACE aili,
apps. AP_INVOICES_INTERFACE aii
WHere aii.invoice_id=aili.invoice_id
AND aili.invoice_line_id=air.parent_id
AND aii.Invoice_num = 'Invoice Number'

Thanks,
MarunK