AVD mutli-session issue

Dear All, 

We just setup a new pool in AVD . Problem it seems that multi-session is not working as exepcted. 

when a user is connected already , the next user has a message asking him if he wants to disconnect the current session. 

We have set the max number of session to 9999 but still the same . 

Thank you 

Regards 

Mchabs