No Accounting Document created in billing plan (date already billed?)

I am trying to issue the final invoice for a sales order, but when creating the final invoice, no accounting document was created.  In the error log, I get the following, which repeats for each item number in the billing document.  I go through the same process each time I issue a final invoice, so I don't know why this is different.

Any help or advice would be greatly appreciated!

XXXXXXXXXX 000010 Date 20151229 has already been billed (billing plan)

Technical data

    Tech. data details

     Client                                 100

     Group Number

     Sales Document Number                  XXXXXXXXXX

     Item Number of the SD Document         000010

     Schedule Line Number                   0142

     Counter in Control Tables              00

     Message Identification                 VF

     System Message Number                  142

     Output Type                            E

     Message Variable 01                    20151229

     Message Variable 02

     Message Variable 03

     Message Variable 04

     Group Type                             F