Solution : https://service.sap.com/sap/support/notes/859304 (SAP Service marketplace login required)
Key words :
srm server=>technical basic settings=>define back-end systems, customizing srm server=>cross-applications basic settings=>enable, make synchronous customizing settings, separate master data record, xi server system, error-free data exchange, srm purchasing system, synchronization occurs asynchronously, master data record, system synchronizes part