Checking Table 'service'   ERROR: 10813...service(number=XXXXXXX): Nextusagedate is '0000-00-00' (FIX MANUALLY)

BillMax support promptly acknowledged that it is a bug that cause this behavior under rare circumstances.  The solution is to run on the billmax database the following SQL:

update service set nextusagedate=invdate where number=<XXXXXXX>;