Re-download the transactions receiving this error. If issue persists, Contact Support and reference this article.
If the re-download of this transaction fails, reference the XML data of the failed transaction for additional information about the transaction. For example, if you view the transaction and see that it was for a 40$ gift submitted by Jane Doe on 1-15-15; you can search revenue records for this constituent and confirm the gift already exists on the record. If so, the duplicate in Failed Transactions can be safely deleted and disregarded.