Solution : https://service.sap.com/sap/support/notes/1611768 (SAP Service marketplace login required)
Key words : 
running user sync report, front-end application, solution kindly implement, symptom invalid characters, user details, user permissions, invalid characters, gracuser table, file system, access request
Related Notes : 
       
| 1613632 | Download Files for Legacy Risk Analysis | 
| 1607067 | Master Note for SAP Access Control 10.0 - Support Pack 6 |