SAP Message 8A551 - Format of reference document number is invalid

Diagnosis You have chosen a document type that is relevant for official Argentinedocument numbering and for which the official document number is notautomatically generated. That means that you have to enter the officialdocument number in the reference field in the following format: XXXXANNNNNNNN XXXX: 4 digit number for the issuing branch A: Printing character NNNNNNNN: 8 digit number field Procedure Please enter the official document number in the format desribed above.Please check also that the printing character entered in position 5 isdefined in your customizing settings of the possible printingcharacters.