Solution : https://service.sap.com/sap/support/notes/496437 (SAP Service marketplace login required)
Key words : 
user-defined info structures, abap error message convt_overflow, sap info structure s039, unusually high price fluctuation, unusually high stock quantity, sap info structures, communication structure mcbest, key figure bwertv, key figure wbwbest, attached program corrections
Related Notes : 
       
| 517182 | CONVT_OVERFLOW after implementation of Note 496437 |