Two (or more) identical billing documents exist for one delivery or order item.
SAP Note 12934 explains that this issue can occur if the user postprocesses terminated update records. If this is not the case, the exact root cause can only be determined by reproducing the issue. See SAP Note 9.
SAP Note 12934 has report ZVINVOIC which can be used to identify double or duplicate invoices.
To repair the statuses of the preceding delivery documents, run report RVDELSTA, after the invoice is deleted. To repair the statuses of the preceding sales documents, run report SDVBUK00, after the invoice is deleted.
Related Note / Content:
12934 - Two billing documents exist for one delivery note