SAP Message V1085 - Date &1 is before the beginning of factory calendar &2

Diagnosis
Billing date &V1& lies before the date on which factory calendar &V2&becomes valid. This calendar is stored in the customer master of thepayer for determining the invoicing period.

System Response
The system does not permit processing to continue.

Procedure
Check
whether the correct year has been entered for the billing date
whether the correct factory calendar has been entered
whether the calendar needs to be activitated for the year.