Invoice Number Already Used

When I am trying to create an invoice I am getting a message to say that "The automatic invoice number generated has already been used, please check your Customer Defaults".  Where is this and why am I getting the Message?

Solution

The message is appearing because the last invoice number has previously been used.  There may have been a delay in relaying this information back to the server.

Please go to Admin / Defaults / Manage Customer Defaults - Invoices and move on the Invoice number as necessary.  On the vary rare occasion intervention by your Partner or Support Staff may be necessary.