Solution : https://service.sap.com/sap/support/notes/513016 (SAP Service marketplace login required)
Key words : 
gjahr    gjahr    4    0    numc    fiscal year            bgjahr    gjahr    4    0    numc    fiscal year     <<<< insert                       activate structure rm08a, system displays s-message m8605, structure rm08a, fiscal year, transaction 'release invoice items', transaction 'change invoice document', gjahr reason, transaction add invoice, invoice verification type '3', conventional invoice verification
Related Notes : 
       
| 193173 | MR2M: Error message F5568 in fiscal year change |