Solution : https://service.sap.com/sap/support/notes/382285 (SAP Service marketplace login required)
Summary : 
      When using SAP WinGUI on a Microsoft front-end, certain characters are replaced by ‘#’, triggering Message 195 which indicates prohibited characters. This issue arises due to character conversion discrepancies between Microsoft front-end code pages (e.g., 1252 and 1251) and SAP back-end ISO 8859 standard code pages (e.g., 1100 and 1500). Characters such as the Euro-Sign and "smart quotes" from MS Word are often impacted. For SAP Unicode systems, all characters entered are supported; however, on non-Unicode systems, users must avoid characters not supported by the system’s code page.
Key words : 
sap front-end code page 1160, sap front-end code page 1504, front-end code page, back-end code page, ms word autocorrect-options, sap system code page 1100, sap system code page 1500, back-end code pages, current system code page, sap system code pages
Related Notes : 
       
| 1375438 | Globalization Collection Note | 
| 1319517 | Unicode Collection Note | 
| 1023437 | |
| 735356 | |
| 439570 | Error message when entering the Euro symbol | 
| 436165 | Characters are displayed incorrectly |