SUMMARY:
There could be scenarios where you have created an invoice for time or expenses entered for specific clients using the "Client Invoice" feature in Web TimeSheet Integration Manager for QuickBooks.
 
However later you find that you would like to edit the invoice for different reasons and recreate the invoice again after making the required changes to the timesheet or expense-sheet.
Transferring the same data and creating the invoice will NOT over-write the previously created invoice.
 
WORKAROUND:
Manually delete the invoice which was previously created in Quick Books and then use the Web TimeSheet Integration Manager for QuickBooks to create it again.