Solution : https://service.sap.com/sap/support/notes/311520 (SAP Service marketplace login required)
Key words : 
additional key words og 866 og_conv_vc, wrong system version entry, contract conversion data gathering, report og_conv_vc abends, error message og 866, conversion report og_conversion_date, sap_appl support package 21, sap_appl support package 12, 0a                     verify, crt installed
Related Notes : 
       
| 208340 | Conversion : IS-SW 2.1A / IS-HT 4.61 overview | 
| 170144 | IS-SW Rel 2.0 and R/3 4.5B Add On Support Packages |