The Sales Order Invoicing process references the Sales Order item line detail, specifically the Delivery and Despatch dates of the items on the Order to determine the Invoicing date. This means that if the Invoice posted by the system when using the Sales Order Invoicing task posts transactions has the wrong date, it is likely that the Order's item information is populated incorrectly.
As with all transactions posted incorrectly, the correct solution is to reverse that transaction and raise a new manual transaction in its place with the correct information. It is important to note that you should not run the Sales Order Invoicing program again to invoice this order as it will not be picked up.
