Solution : https://service.sap.com/sap/support/notes/74791 (SAP Service marketplace login required)
Key words : 
period indicator 'posting period', solution repair member lm61wf04, incorrect forecast date, material master mm01, additional key words, program error, note 74791 requires, note 41493, calculated, prerequisites
Related Notes : 
       
| 89555 | Forecast date for fiscal year variant MM01 | 
| 41493 | Deact. interactive forecast for daily period split |