Over the last 8 months we have had staff changes and payments were entered incorrectly. Some payments were entered with order numbers and some with invoice numbers; some have been entered as negative numbers and some positive. In any case many customers' accounts are not balancing and the Overdue Receivables and Aged Trial Balances are totally messed up. Nothing is reconciled - payments are not applied to the correct invoices. One person entered a total payment for several invoices but they are still showing as unpaid because they were not applied to the specific invoices. I also believe that some batches were entered twice because invoices are showing as negative numbers in the Over 90 days overdue column. Is there any way to correct this?

It sounds like you will have to spend some time disentangling the more complex entries.

The starting point (after making a backup) is to locate the situations where there are unapplied Cash receipts that match exactly to invoices (in other words, they should have been applied at the time of entry). Enter a $0.00 Receipt and "apply it" to both the cash receipt and invoice transactions. That will clear up a number of the entries and allow you to focus on the more complex situations.

Thank you - it's a start.