Maybe the new licensing components were not installed properly. Could you please run c:\Program Files\Maxon Cinema 4D 2023\plugins\C4DtoA\arnold\license\installer\Autodesk_Licensing-13.0.0.8122_01.exe and try to sign in again? It should open the web browser now and ask you to login to you Autodesk account.
If that does not help, could you please run File > Diagnostics... and send us the log files? Click on Open Log Folder to locate the file.
// Peter Horvath
// C4DtoA developer
