The problem is a corrupted batch/invoice. During entry, likely when adding or deleting items on invoices, the invoice total did not get updated on the removal of the item. I am surprised that a Data Interity Check would not have found this error in the Open Batch, as it did in the Archived Batch.

Some item for 54.55 was added to the invoice, but this amount did not get added to the invoice total for some reason.

As this has only happened twice in presumably hundreds of invoices or more, the problem is either a very specific set of keystrokes, or your workstation/network cannot keep up with the speed of the entry clerk.