Assetto Car Tuner does not work

[Gaudin de Beaufort]

When i select the "common" folder in the "steamapps" folder in Assetto Car Tuner, I get the "right folder was not selected" message.
Assetto Corsa is installed in this folder !
Does anyone know what's going wrong ?
Thank you in advance for your responses !

 

[tater tots]

gear ratio setting not working