@astlaurent This problem occurs because Windows (I assume you use Windows 10) uses the actual windows account to login into SMB-Shares. Normally you should then be remapped to a an guest account (because recalbox does not know you windows user), but Windows seems not to accept it and denies the access to the network share or the remapping from samba does not work correctly. I did not investigate further. Anyway, if you remove the "map to guest=bad user" property from smb.cfg at the recalbox, Windows will ask you for login information.
Hi well didn't receive a reply, but worked it out by myself, pretty obvoius really. For any newbie who has the same question and comes here looking for an answer:
In Network settings: Enable Wifi: ON, Wifi SSID: wifi user name, Wifi Key: wifi password. Then back to Main Menu > Quit > Restart System.
Hope this helps someone