PROBLEM: "You may not create or edit a transaction dated on or before the dividing date."
SOLUTION: The dividing date is the date you gave a copy of your QuickBooks to your accountant.
No invoices or estimates dated earlier than the dividing date can be updated by InvoiceASAP, because your accountant is working on your invoices & estimates in this time period.
Once your accountant merges his changes back into your QuickBooks, then the sync will be able to update these invoices/estimates, and the error will go away.
You can also exclude the invoices getting this error by using the Advanced Toolbox.
If you don't have access to the Advanced Toolbox, please submit a support ticket to InvoiceASAP and request access to the Advanced Toolbox in order to exclude invoices or estimates from your sync.